This study investigated the concrete-to-concrete friction behavior under dynamic cyclic loading at different loading rates, vertical loads, and surface roughness. The present work answers essential questions about the dynamic behavior of concrete-to-concrete friction since most of the available literature deals with static or quasi-static loading conditions. To this end, an experimental program was devised by casting 96 concrete blocks. A total of 48 dynamic push–pull tests were performed on each pair of blocks (mobile top block and fixed bottom block). Test variables included three types of surface roughness, four different loading rates, and two normal stresses. Performance measures included the static and dynamic friction forces coefficients of static and kinetic friction in addition to effective stiffness and effective damping. Moreover, the test results showed that the static and kinetic friction coefficients, effective stiffness, and effective damping decrease with increasing loading rates. Moreover, increasing the normal stress increases the friction force, thus increasing the effective stiffness and reducing the effective damping surface for all surface roughness types. The effects of test variables on the hysteresis behavior were also investigated. Notably, in reinforced concrete structural members at the stage after the failure of the interface, composite action no longer exists. At this stage, the friction between the two concrete parts should maintain a residual shear strength that, if quantified accurately, would help to avoid catastrophic failures of the concrete structures2. The saw-tooth model is commonly used to illustrate the fundamental concept of this theory2  two concrete elements cast at different periods; (b) support and concrete elements; and (c) two portions of concrete elements resulting from a crack3. They stated that the shear stress in rough surfaces produces tensile stresses in the reinforcement crossing the interface, resulting in compression in the joint. Also, the study compared the predicted ultimate shear stress, using shear friction theory, with the experimental results collected from previous studies and concluded that the theory successfully predicts the maximum shear stress at concrete interfaces. In addition, the shear friction theory was used to design knife and bearing connections, which were effectively used in structures, and concluded that the theory is also helpful in the design of connections. After this, Mattock and Hawkins4 proposed a modified shear friction theory (MSF) which included a term to account for the adhesion at the concrete interfaces. The ACI approach is partly based on this theory. Later on, the extended shear friction theory (ESF) was considered by the CEB-fib Model Code 20105. This theory evaluated the critical effect of adhesion, friction, aggregate interlock, and dowel action mechanisms and captured their relationship by introducing interaction factors6.Shear friction theory (SF) was first proposed by Birkeland and BirkelandThe current study reports the results of an experimental program conducted to investigate the behavior of the concrete-to-concrete friction and the capacity at the interface between two concrete blocks cast at different times under cyclic loading. This test represents the case after the failure of the interface. The composite action is no longer established at the concrete-to-concrete interface, and the resistance is governed only by friction. In particular, the effects of the test rate, normal load, and surface roughness type on the bond strength and shear capacity are investigated.7 performed static push-off tests to investigate the shear friction at the interface between high-strength precast elements and normal-strength cast-in-place concrete blocks. The authors showed that the shear capacity at concrete interfaces could be divided into three mechanisms: friction, dowel action, and adhesion explained in more detail in8. Adhesion occurs due to the chemical bond at the interface between the concrete elements cast at different times. While an extreme strength is attained, debonding occurs at the interface between concrete elements. When a compression force is applied to the interface, the shear forces will be transmitted by friction. While the concrete elements are increasingly displaced relative to each other, the dowels that cut across the interface will be under tension, and yielding may occur. Hence, the dowels will exert compression force, and the shear forces will be transmitted by friction8.The friction behavior at the concrete-to-concrete interface has been the subject of many studies to understand the mechanisms of shear capacity and the contribution of each mechanism in each stage. For instance, Zilch and Reinecke9 conducted direct shear tests on concrete interfaces while considering the normal stress, dowels, and coupling effect. The authors concluded that adding reinforcement and normal load increases the direct shear resistance and changes the behavior from brittle to ductile9; this is in line with the ESF theory that distinguishes between brittle (adhesive bond–based) and more ductile (addition of reinforcement) behavior6. It was also concluded that the friction, cohesion, and reinforcement action ratios are identical at the final residual stage9.Additionally, Xia et al.10 tested the behavior of RC beams, with concrete interfaces located in the hogging part, under cyclic loading with increasing amplitude. The study concluded that casting interfaces have no effect on the strength of the structural member but can reduce the ductility of the structural member. In addition, it is concluded that the reinforcement and the direction of the interface do not affect the behavior. Furthermore, Cavaco and Camara11 experimented with evaluating the behavior of concrete interfaces submitted to a combination of bending moment and shear. The authors concluded that the load transfer capacity is decreased at the interface because of the cracks initiated by the bending moment, which led to the partial reduction in ductility but did not affect the strength of the specimens. To accommodate for the ductility loss in RC structures at the concrete interfaces, many studies investigated special detailing at concrete-to-concrete interfaces to improve the ductility. One of these studies was by Cavaco et al.12, who tried different details to enhance the ductility at the concrete-to-concrete interfaces. This study concluded that providing web reinforcement, normal to the concrete interfaces, can improve the ductility by limiting the shear slippages. Another study by Sørensen et al.13 investigated the effectiveness of a new shear connection at concrete interfaces for precast RC shear walls. In this design, the interfaces between precast parts are indented and attached by grouting with mortar. Also, the interfaces are reinforced with U-bar loops, which are overlapped and parallel to the wall plane. According to the results of the push-off experiment, it is concluded that the ductility is significantly improved using the new connection compared with the typical shear connection.Many studies have been performed to study the behavior of reinforced concrete (RC) structures, with concrete-to-concrete interfaces, under cyclic loading. For example, Cavaco et al.15 presented some formulas to design concrete-to-concrete interfaces2. The CEB-fib Model Code 20105 includes design recommendations for rigid and non-rigid bonds at concrete interfaces based on recent research2. Randl6 clarified the theory behind this and concluded that considering the recommendations based on bond type, along with the detailing requirements, forms the design of the concrete-to-concrete interface, taking into account the different mechanisms at the interface.Based on previous major studies that evaluated the behavior of shear friction at the concrete interfaces, design codesTo understand the behavior of concrete parts sliding relative to each other, it is necessary to consider several variables, such as the surface finishing, loading rate, and normal stresses. Studying the concrete-to-concrete friction behavior under different test variables allows us to predict the shear capacity with better accuracy.17. To determine the shear capacity at the concrete-to-concrete interface, design codes such as ACI 31815, Eurocode 214, and CEB-fib Model Code 20105 recommend different approaches to characterize the degree/level of roughness.The surface roughness affects the strength of the bond, cohesion, and friction at the interface between concrete parts16 carried out an experimental program to examine the shear capacity at the concrete interface with multiple surface roughness types of the concrete surface. The concrete surface was prepared by chipping with a jackhammer, wire-brushing, sand-blasting, and left as-cast using a formwork made out of steel. Additionally, pull-off experiments were performed to examine the bond strength under tension. From these results, it was concluded that the extreme strength value of the bond was obtained with sand-blasting and prewetting, and the substrate surface does affect the strength of the bond. Another study performed by Santos et al.17 investigated the possibility of quantifying the roughness of the substrate surface and correlating it with the interface bond strength. The results demonstrated that the roughness parameters are linearly correlated with the bond strength and that surfaces with higher average roughness values have higher bond strength.Concerning the surface roughness effect, several studies were conducted to quantify the correlation between the roughness of concrete surfaces and the strength of the bond between concrete parts cast at different periods. These studies included experiments to study the concrete-to-concrete friction behavior under static loading. For instance, Silva et al.18 investigated the frictional behavior of plain concrete interfaces through small-scale monotonic and cyclic displacement-controlled laboratory tests. Their investigation considered the roughness and normal loads as test variables. The effect of these variables on the friction coefficient and shear capacity at the interface was investigated. The results showed that the shear capacity decreased due to surface grinding and that the coefficient of friction decreased under dynamic loading conditions. Fronteddu et al.19 conducted a shear test on concrete lift joint specimens with various surface roughness types to compare sliding joints’ static and dynamic behavior. Their test results showed that the coefficient of friction decreases with increasing normal load under both dynamic and static shear forces and that the shear strength depends on the surface roughness.Previous experimental studies on the concrete-to-concrete friction behavior, which included tests under dynamic loading conditions, investigated the effect of different test variables on the interface’s capacity between concrete surfaces. For instance, Tassios and Vintzeleou20. They experimentally studied the shear behavior at the interface between a cast-in-place slab and a precast beam under monotonic and dynamic loadings with variable and constant amplitudes. High amplitude loading was the leading cause of interface failure due to increased cracking and concrete cover separation. However, low amplitude dynamic loading was shown to lead to failure in the steel bar because of fatigue as the shear strength decreased sharply. However, no evident damage was noted in the concrete during the tests.Previous dynamic tests also include the work of Figueira et al.21. These include the work of Tassios and Vintzeleou18, which investigated the friction behavior of interfaces under monotonic and large reversed displacements, and that of Fronteddu et al.19. They also examined the friction behavior under static and dynamic loading. However, neither of these studies assessed the variation in friction force under the effect of different loading rates. Furthermore, only a few published experimental-based studies in this field investigated the behavior of concrete-to-concrete friction after the failure of the shear connection and its implications on the horizontal shear strength of the system, such as the one done by Leblouba et al.1. They investigated the behavior of the connection between precast concrete deck panels and concrete girders but did not consider different surface roughness types.Most studies on concrete-to-concrete friction behavior are based on static and quasi-static loading conditions. Experimental studies investigating the behavior of concrete-to-concrete friction under cyclic loading with different concrete surface roughnesses are scarceThe damping of reinforced concrete structures is a complex phenomenon. It is approximated in the range of 2–5% of the critical damping based on the observed overall behavior of structures. It is known that the friction in cracked sections contributes to the bulk of this damping. Therefore, characterization of the friction at the concrete-to-concrete interface is of paramount importance towards a systematic and objective quantification of damping in reinforced concrete structures.Conduct dynamic cyclic push–pull tests on concrete block specimens and study the concrete-to-concrete friction behavior.Assess the effect of concrete surface roughness on the behavior of horizontal shear strength at the interface.Study the effect of loading test rate on the behavior of the horizontal shear strength at the concrete-to-concrete interface.Study the effect of additional normal stresses on the horizontal shear strength at the concrete-to-concrete interface was studied.Investigate the variation of static and kinetic friction coefficients, effective stiffness, and effective damping with the loading test rate, surface roughness, and normal stress.Considering the above, the objectives of this research are to:In this section, the experimental work is presented. In total, 48 dynamic push–pull tests were carried out to investigate the friction behavior of the concrete-to-concrete interface. In what follows, the geometry and mechanical properties of the test specimens are presented along with all test variables.Each test requires a pair of concrete blocks, one at the top, the moving part, and one at the bottom, the locked-in-place part. The geometry and dimensions of each block are presented in Fig. The top block has 400 × 350 × 90 mm dimensions with two holes for the long bolts that hold the block to the actuator’s head. The fixed bottom block has dimensions of 400 × 400 × 90 mm.The bottom surface of the top moving block was left as-cast, i.e., the surface was not disturbed. However, the top surface of the bottom fixed block was altered to achieve three types of surface roughness: smooth , medium rough, and rough (achieved by raking the surface with a trowel). A smooth surface is achieved by finishing the surface with a typical finishing trowel, as shown in Fig. As mentioned earlier, 48 tests were run using 96 concrete blocks . The test variables included the test rate, normal stress, and surface level of roughness. As reported in Table 22, while splitting tensile strength tests were performed as per ASTM—49623. At seven days, the average compressive strength was determined to be 31.0 MPa and at 28 days was 43.7 MPa. The average splitting tensile strength of the concrete was determined to be 3.1 MPa at seven days and 4.2 MPa at 28 days.All test specimens were cast using ordinary concrete. The concrete mix proportions were designed to achieve a compressive strength of 40.0 MPa  using steel plates and long bolts to transfer the exerted dynamic load and avoid overturning. The complete test setup is shown in Fig. For the instrumentation, two linear variable differential transformers (LVDTs) were used to ensure the integrity of the lab experiments. The first LVDT was attached to the actuator’s head for quality control of the experiment, while the second LVDT was attached behind the U-shaped steel set up to detect any movement of the bottom block, which was supposed to be fixed throughout the test.2), the coefficient of dynamic/kinetic friction  surface, there was minimal grinding of the concrete surface after the test, as demonstrated in Fig. Moreover, there was a clear cutoff of the surface asperities during the push–pull test in the rough specimens. This leads to the reasonable conclusion that increasing the average roughness of a surface leads to a greater surface deterioration after a push–pull test. In general, it is noted that increasing the test rate results in a higher surface deterioration in the medium rough and rough surfaces, while the deterioration at different loading rates for the smooth surface remains approximately the same. Also, images were binarized to estimate the ratio of white pixels to the total number of pixels to quantity and the difference in the state of surface deterioration before and after the test. After processing images after tests, the percentage of the white area to the total image area was 10.3% for the smooth surface concrete specimen, 57.6% for the medium rough, and 83% for the rough. These results indicate the level of surface grinding and deterioration experienced by concrete surfaces after tests depending on their original roughness level.18. They stated that for a shear stress value less than the one needed for the overriding of asperities, the shear resistance of the protruding asperities under high normal stress might be more than the tensile strength of the matrix. Therefore, a diagonal crack through the concrete matrix may occur before the overriding of the asperities, which will result in a premature failure mechanism. Moreover, Cavaco and Camara11 noted the diagonal cracks. They mentioned that this happens due to the decreasing friction capacity, which reduces the ability of a structural element to transfer shear loads.It is interesting to note that for some specimens, some cracks were developed at the edges under vertical stress of 0.25 MPa, as shown in Fig. 25:The breakaway effect before load reversal is represented by a rapid increase in the friction force at the beginning of the relative movement or each motion reversal, followed by a quick force release. The static friction condition and the stick–slip are the leading causes of this effect.The cycling effect is represented by the continued reduction of the friction force with the repetition of cycles.Figure The velocity effect is represented by the friction force variation with the velocity. A speed reduction is expected to introduce lower values of friction force. This reduction can be noticed in the rounding of the shape of the loops when reaching the peak displacement.The frictional force and the applied vertical load are directly proportional according to the simplified Coulomb model in which the effect of sliding velocity is not considered. This assumption leads to a rectangular force–displacement hysteresis loop that differs from the typical experimental loop shape shown in Fig. The friction force versus the horizontal displacement curves for a subset of test specimens are shown in Figs. At the beginning of the first loading cycle, the horizontal load increases until the top block moves relative to the bottom block. This load represents the static friction, which is used to estimate the coefficient of static friction. This load decreases in subsequent loading cycles, indicating the kinetic friction phase at which the coefficient of kinetic friction occurs. It is important to note that the friction force is higher in the unloading phase of the first cycle than in the loading phase . The friction force decreases significantly after each cycle . The medium rough surface tests represent an average case where the friction force decreases rapidly but not as much as the rough surface tests. This is the case in most tests with 0.25 MPa additional pressure. This trend is due to the effect of the vertical pressure applied on the test specimens and its reduction rate for each surface roughness. As we will see later, the vertical force decreases rapidly and significantly with each loading cycle in rough surface tests but decreases slowly and slightly in smooth surface tests. Even though the shape of the hysteretic loops is different for different loading rates, the effect of the test rate on the strength of the test specimens is not noticeable see Fig. .Previous experimental studies showed that the load-velocity graph follows the typical hysteresis shape shown in Fig. 26, and nonidentical slopes of friction force for the deceleration and acceleration phases characterize the non-reversibility27. Nonreversibility was noticed in many experiments . The presliding displacement occurs due to the friction force’s spring-like behavior before the actual relative sliding or, in other words, due to the tangential stiffness at the contact interface between the bodies29.The presliding displacement and the non-reversibility of the friction force are the most important phenomena that can describe the behavior of the load-velocity graph. The small hysteresis around the zero relative velocity describes the presliding motion19, in which the velocity starts from zero and then increases to reach a maximum value; then, the motion is reversed. It was observed that the S portion occurred when the upper concrete block slowed down for shear load reversal. As expected, increasing the vertical stress increases the hysteresis loop area since (as demonstrated in Sect. 5.2) increasing the vertical stress increases the friction force.The general behavior of the load-velocity graph takes the shape of the letter S, as shown in Fig. 18 investigated the concrete-to-concrete friction behavior under cyclic loading. In their tests, the authors maintained almost constant normal stress. However, it was noted that normal stresses also increase in real reinforced concrete structures when an interface is subjected to shear. Together with shear displacement and crack width, normal stresses are expected. Hence, the tests were performed under free normal stresses to represent a real scenario. It is clear that vertical load changes throughout the test. As specimens are loaded horizontally, the vertical load goes up and down depending on the magnitude of dilation and direction of displacement. In the beginning, the vertical force decreases. After the failure of the aggregate interlock mechanism at the concrete-to-concrete interface and as the shear displacement increases, the top block overrides the asperities and loose aggregates at the interface, which increases the tendency to cause dilation and increases the crack width. This, as a result, causes an increase in the normal load recorded by the vertical load cell since the specimen is restricted from moving in the vertical direction.At the beginning of each test, two different vertical stresses were applied to the top concrete block 0 and 0.25 MPa. The load cell placed above the top concrete block monitored the vertical force during tests. The shear test configuration ensures that the normal stresses at the interface are free to vary with the horizontal shear displacement. Tassios and Vintzeleou31.Additionally, it is noted that increasing the test rate resulted in a greater reduction in the vertical force at the end of the test for both medium rough and rough surfaces. This agrees with the observation of higher degradation of medium rough and rough surfaces at higher loading rates, which will result in a reduction in the recorded vertical force. In general, it is noted that the decrease in the vertical force was the lowest for the smooth surface, taking into account all loading rates, and the reduction was higher for the medium rough and rough surfaces, as shown in Fig. For the tests where vertical stress of 0.25 MPa is applied, all test specimens start with almost similar vertical forces regardless of the surface condition, approximately 35 kN . However, this force decreases rapidly with the surface roughness. In smooth surface tests, the effect of the test rate is negligible; at all speeds, the vertical force reduces slowly with time. In medium rough, and rough surface tests, the effect of the test rate is substantial between a 2 mm/s test rate and 5 mm/s. However, above the 5 mm/s test rate , the test rate has a negligible effect, especially in rough surface tests. This is illustrated in Fig. a smaller), and as a result, the vertical load decreases. This behavior continues with subsequent load cycles where the vertical load increases and decreases. However, the overall trend is that the vertical load decreases after each complete load cycle. This is illustrated in Fig. 32.Usually, in a test involving a perfectly smooth surface, the vertical load should remain the same regardless of the test rate. However, in the case of rough surfaces with many asperities, the top block, when pushed, moves up, thus increasing the vertical force (reaction of the downward jack). During load reversal, some of the asperities are reduced in height  for tests performed under 0.0 MPa additional normal stress and slower (between 5 and 20%) for tests done under 0.25 MPa additional normal stress.Experimental data for tests under 0.0 MPa and 0.25 MPa additional normal stress showed that, in general, increasing the test rate decreases the coefficients of static and kinetic friction, as shown in Figs. 1. The effective stiffness is the highest in smooth surface tests due to the lower height of asperities than on rough surfaces. The decrease in effective stiffness was between 14 and 27% for tests performed under 0.0 MPa additional normal stress and 8–12% for tests performed under 0.0 MPa additional normal stress. Similarly, the effective damping . Regarding wire-brushed and raked surfaces, the experimental static coefficient of friction values best fits the range of the rough surfaces (0.7–1.0). It can be noted that there are some differences between the experimental and CEB-fib Model code ranges due to many possible reasons. One of the reasons might be the imperfection of the concrete surfaces. The design codes should consider this by providing statistical parameters  based on extensive experimental data rather than providing exact ranges. Also another reason might be the use of different techniques for roughening the concrete surfaces compared with the CEB-fib Model code. This can be the case in rough surfaces where the CEB-fib Model code mentioned roughening methods (sand-blasted and high-pressure water blasted) are different from those used in this study.The average coefficient of static friction varies between 0.5 and 0.9 for the as-cast surface and between 0.7 and 1.1 for wire-brushed and raked surfaces. Compared with CEB-As concluded previously, higher normal stress increases the friction force for all tests. Figure For instance, in rough surface tests, the ratio Concerning the concrete surface condition after the test, surface deterioration was higher on rough surfaces than on smooth surfaces.The most common friction phenomena related to the load–displacement hysteresis loop and load-velocity hysteresis loop  were observed across all dynamic push–pull tests.With time, the vertical load behavior depends on the surface roughness; on rough surfaces, a noticeable decrease in the vertical load was observed compared with the smooth surface. This trend confirms that the degradation on rough surfaces is higher than that on smooth surfaces, leading to a decrease in the recorded vertical load.The vertical load time history depends on the test rate on rough surfaces. The vertical load decreases noticeably at higher loading rates.The static and kinetic friction coefficients, effective stiffness, and effective damping decrease with increasing loading rates.Increasing the normal stress increases the friction force, thus increasing the effective stiffness and decreasing the effective damping for all surface roughness types.In this paper, we presented the results of an experimental program involving 48 dynamic push–pull tests of concrete specimens placed on top of each other. All specimens were subjected to dynamic cyclic displacement loading with varying rates , varying normal stresses (0 and 0.25 MPa), and varying surface roughness . From this study, the following conclusions are drawn:The study of concrete-to-concrete friction is essential; quantifying the friction and taking it into account is necessary to design composite structures and concrete members subjected to shear. ACI 318, AASHTO, CEB-fib model code, and Eurocode all provide shear design equations that consider the coefficient of friction. These codes give the coefficients of friction for different concrete surface conditions in the form of tables. However, all present design codes consider only the case of static friction and ignore the kinetic friction.The effect of loading rate and normal stress on the coefficient of friction and capacity of the interface should be considered in the provisions of design codes.Rough surfaces that are widely used in construction practice should be favored in structures subjected to cyclic loading, taking into account the decrease in coefficient of friction with loading cycles.Therefore, based on the results of this study, the following is recommended:Future research recommends expanding the current study to include higher stresses and lower and higher loading rates.


Moreover, before degradation, concrete with polypropylene fiber shows high fracture energy and decent residual strength of 1.9 MPa when a 3.5 mm crack appears. The tests showed a compressive strength decrease in all compositions with shrinkage reducing additives and its combinations after 28 days of hardening.This paper analyzes the efficiency of shrinkage reducing additives for the shrinkage deformations of ordinary Portland cement (OPC) concrete and its mechanical properties. OPC concrete was modified with an organic compound-based shrinkage reducing additive (SRA), quicklime, polypropylene fiber, and hemp fiber. It was found that a combination of 2.5% quicklime and 1.5% SRA led to the highest reduction in shrinkage deformations in concrete, and the values of shrinkage reached up to 40.0%. On the contrary, compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. Hemp fiber did not show a significant shrinkage reduction, but it is an environmentally friendly additive, which can improve OPC concrete flexural strength. Polypropylene fiber can be used in conjunction with shrinkage reducing additives to improve other mechanical properties of concrete. It was observed that 3.0 kg/m Concrete is one of the most common building materials in the world due to its affordable price and particularly good mechanical properties. Nowadays, wide concrete surfaces with wide open surfaces are especially popular in the concrete industry: thin-walled structures, monolithic elements of bridges, or seamless floors. During the hardening of OPC concrete, shrinkage deformations may occur which could lead to various undesirable cracks and fissures. Many scientists are looking for ways to reduce or eliminate the shrinkage of concrete without changing the main properties of concrete ,13,14,15Shrinkage of concrete can be described as a decrease in volume, regardless of its consistency, which can result from a variety of chemical reactions or a decrease in relative humidity or a slightly saturated porous system. Deformation of materials is often divided into chemical, plastic, carbonization, autogenous, and drying shrinkage and depends on the initial setting time and hydration mechanism . In the Many authors report that an effective way to reduce shrinkage deformations is to use fibers and shrinkage-reducing additives that improve the properties of concrete ,16,17,18Many studies ,7,8,9,10Many authors ,14,15,16Çomak et al.  studied The aim of this study was to investigate the effectiveness of various additives and their combinations in monitoring the influence of shrinkage deformations on concrete mixtures and its mechanical properties. OPC concrete was modified with SRA (organic compound shrinkage reducing additive), quicklime, polypropylene, and hemp fiber to determine the effect of different additives on the properties  of the fresh concrete mix and mechanical properties and durability of hardened concrete .2/kg was used. The powder of quicklime CL 90 with the fineness of 300 m2/kg and reactivity class R5 was incorporated. The amount of quicklime was 1.5% and 2.5% (wt. of OPC) The chemical composition of OPC and quicklime is presented in Ordinary cement CEM I 42.5 R with the fineness of 390 mThis experimental study was performed using hemp and polypropylene fibers, and liquid phase shrinkage reducing agents (SikaControl −50) as well. In all mixtures, the same water/cement ratio of 0.53 was applied.3, while fine aggregate sand (fr. 0/4 mm) with its particle density of 2650 kg/m3 was incorporated. In all concrete mixtures, the same amounts of coarse and fine aggregates were added . The particles size distribution of concrete aggregate is shown in Coarse aggregate gravel (fr. 4/16 mm) was used with its particle density of 2600 kg/m3, melting point of 160–170 °C, tensile strength of 500 MPa, tensile modulus of elasticity of 5.2 GPa, length of 38 mm, and diameter of 0.7 mm. Hemp fiber has a density of 0,16 g/cm3, melting point of 140 °C, length of 30–60 mm, and diameter of 0.6 mm. For this research, 3 kg/m3 of each fiber were used in concrete.To reduce the amount of water in concrete, polycarboxylate polymer-based SP (superplasticizer) was used. The admixture has the density of 1.06 ± 0.02 kg/l, pH of 4.4 ± 1, total chloride ion content of <0.1%, and equivalent sodium oxide content of <0.4%. The dosage of superplasticizer was 0.5% (wt. of OPC). SRA based on organic compound has the density of 0.935 ± 0.02 kg/L, total chlorine ion content of <0.1%, and equivalent sodium oxide content of <0.5%. The dosage of SRA was 0.5% and 1.5% (wt. of OPC). Two types of fiber (polypropylene and hemp) were incorporated in the concrete. The density of polypropylene fiber was 0.91 g/cmUnder the laboratory conditions, various mixtures  were madBy combination of initial materials, 11 different mixture compositions with the same water/cement ratio (0.53) were prepared .The granulometry of aggregates was performed according to EN 933-1 .Three fresh concrete tests were made: the slump was determined following standard EN 12350-2, air content of compacted fresh concrete according to standard EN 12350-7, and the density of fresh concrete according to standard EN 12350-6.The concrete mixtures were prepared in the “Zyklos” concrete mixer. The specimens were formed following standard EN 206. The sizes of specimens were standard cubic (100 × 100 × 100 mm) and prism (75 × 75 × 250 mm) which compacted on the vibrational table. The specimens were hydrated for about 20 h in the molds, and, after that they were demolded, cubic specimens were cured in water for 28 days, while prism specimens were cured in air for 90 days.Six hardened concrete tests were made: the density of hardened concrete specimens was determined according to standard EN 12390-6, the compressive strength of hardened concrete according to following standard EN 12390-3, and the flexural strength of hardened concrete according to standard EN 12390-5. Concrete fracture energy was calculated according to CMOD (crack mouth opening displacement) curves. Areas under the CMOD curves were found by using the “Originpro” software . The shrThe concrete prism weight was evaluated after 3, 7, 14, 28, 56, and 90 days of hardening, and the change in mass of concrete was calculated according to the following Equation (2):Freeze-thaw resistance of concrete was determined by volumetric freezing after immersion in water following Lithuanian standard LST 1428.17:2016 . This teFreeze-thaw resistance and porosity parameters test methods are very well described in the literature .The microstructures of fibers and hardened cement pastes were determined according to scanning electron microscopy with a high-resolution scanning electron microscope (ZEISS EVO MA10).Test results showed an obvious change in the workability of fresh concrete properties  when difA reference mixture slump value was 180 mm, resulting in the high workability of the S4 slump class. Most of the batches with earlier mentioned additives have the same or lower slump value than the reference mixture. The slump increased to 190 mm for concrete mixtures with 0.5% and 1.5% (wt. of OPC) of SRA. SRA slightly improved the workability of the concrete mixture because this additive reduces surface tension of the mixing water in the liquid stage, and free water appears in the fresh mixture. A similar explanation is provided in a previous study . Concret3; air content was 3.4%. Compared to the reference mixture, most of the selected shrinkage reducing additives did not have a significant influence on fresh concrete density. The highest density was obtained in concrete with 1.5 (% wt. of OPC) SRA, and the lowest in concrete with 3.0 kg/m3 hemp fiber. The highest air content was also obtained in concrete with 3.0 kg/m3 hemp fiber. High air content leads to an assumption that hemp fiber creates interaction between fresh concrete density and air content. The following study [The fresh concrete density for a reference mixture was 2356 kg/mThe change in compressive strength of concrete modified with different additives  and their combinations is given in 3 polypropylene fiber (POL3.0) reduced compressive strength by 2.8% and 0.9% after 7 and 28 days, respectively. Similar results were obtained in the study [The experiment revealed that the modification of concrete with additives had a significant effect on the compressive strength of the concrete. Reference specimens (CNTRL) without additives had the average compressive strength of 42.5 and 45.5 MPa after 7 and 28 days, respectively. The used additives led to the decrease in compressive strength after 7 and 28 days of hardening. Polypropylene fiber slightly reduces the strength of concrete after 7 and 28 days when compared with the reference mixture. Specimens with 3.0 kg/mhe study  where po3 hemp fiber (CNB3.0) reduced compressive strength by 6.1% and 7.9%. The following study [3 hemp fiber, 2.5% quicklime, and 1.5% SRA (CNB3.0Ca2.5SR1.5). Compressive strength was reduced by 15.3% and 16.9%.Specimens with 3.0 kg/mng study  observatSpecimens with 0.5% shrinkage reducing admixture (SR0.5) reduced compressive strength by 10.1% and 5.3% after 7 and 28 days, respectively. Specimens with 1.5% shrinkage reducing admixture (SR1.5) decreased compressive strength by 12.2% and 7.9%. It can be assumed that the more SRA admixture that is in the concrete, the greater the reduction in compressive strength. the observation was made that SRA slows concrete hydration reactions; in this way, slow formation of calcium silicate hydrate (C-S-H) causes a decrease in compressive strength .The addition of 1.5% quicklime powder (Ca1.5) reduced compressive strength by 4.5% and 6.2% after 7 and 28 days, respectively. Specimens with 2.5% quicklime (Ca2.5) reduced compressive strength by 6.8% and 8.1%. It is assumed that a small amount of quicklime does not cause a huge loss in compressive strength but overdosing (>2.5% wt. of cement) can be expected to reduce the compressive strength quite sharply. The slowdown in the growth in compressive strength may be due to the high expansion stress generated by the hydration of quicklime .The combination of quicklime and SRA reduced compressive strength even more. When 1.5% of quicklime and 1.5% of SRA (Ca1.5SR1.5) were used, compressive strength after 7 and 28 days was reduced by 12.9% and 10.3%, respectively. Moreover, when 2.5% of quicklime and 1.5% of SRA (Ca2.5SR1.5) were used, compressive strength after 7 and 28 days was reduced by 14.1% and 12.3%. It can be assumed that SRA and quicklime acting together can have an even greater negative effect on the compressive strength of concrete than acting alone.3 was recorded in the composition SR1.5 and the lowest of 2307 kg/m3 in the composition CNB3.0Ca2.5SR1.5. Observing that the densities of the specimens containing 3.0 kg/m3 of hemp fiber were lower, it was decided to determine the relationship between the specimen density and fresh concrete air content  and their combinations is given in 3 polypropylene fiber, 2.5% quicklime, and 1.5% SRA (POL3.0Ca2.5SR1.5) showed the highest increase in flexural strength of 11.7%. Meanwhile, specimens only with 3.0 kg/m3 polypropylene fiber (POL3.0) showed the lowest values of flexural strength results; it decreased by 18.1%. At the design stage of the concrete compositions, an increase in flexural strength was expected to be seen in both compositions with polypropylene fiber, as in the study [Reference specimens (CNTRL) without additives had the average flexural strength of 7.7 MPa. The incorporation of polypropylene fibers in concrete had contradictory results. Specimens with a combination of 3.0 kg/mhe study . A decrehe study .3 hemp fiber (CNB3.0) increased flexural strength by 6.5%. The surface of hemp fiber is rougher than the surface of polypropylene fibers  reduced flexural strength by 9.1%. It is assumed that a small amount of SRA does not negatively affect flexural strength but overdosing (≥1.5% wt. of OPC) can negatively affect concrete flexural strength. Similar flexural strength results were obtained with quicklime powder. Specimens with 1.5% quicklime (Ca1.5) increased flexural strength by 2.6%, and a large amount (2.5%) of quicklime (Ca2.5) decreased flexural strength by 3.9%.Concrete potential against fracture was determined by calculating fracture energy, according to study . In this3 polypropylene fiber: (POL3.0)646and 741 N/m, (POL3.0Ca2.5SR1.5)871 and 1050 N/m. The specimen (POL3.0Ca2.5SR1.5) reached the maximum flexural strength (8.5 MPa), and the specimen cracked but did not experience rapid rupture and continued to withstand the flexural load. The specimen withstood 26.7% of the maximum flexural load at the 0.5 mm crack and 27.2% at the 3.5 mm crack. This phenomenon is explained by the fact that, when the specimen is no longer able to withstand a high flexural load, a crack appears. Under continued loading, the width of the crack gradually increases, but as the crack opens, polypropylene fibers in the concrete structure engage and prevent the specimen from flexing completely. Thus, for this reason, specimens with polypropylene fiber have a residual flexural strength and a high fracture energy. Polypropylene fiber is a great choice to protect concrete from sudden cracking. This fiber is evenly distributed in the concrete, thus creating a kind of 3D grid, so it has excellent reinforcement properties of concrete, which help to take over concrete tensile stresses. Sudden cracking was observed in specimens with 3.0 kg/m3 (CNB3.0 and CNB3.0Ca2.5SR1.5) hemp fiber. The specimens did not reinforce concrete properly, and fracture energy was minimal. It is assumed that in order to avoid sudden concrete breakdown, it is advisable to choose polypropylene instead of hemp fiber, because polypropylene fiber absorbs tensile stresses and has a high fracture energy.A free-drying shrinkage test was performed on all the specimens, as shown in The percentages of shrinkage reduction, when compared to reference specimen results, after 7, 28, and 90 days are given in After analyzing the obtained research results, it could be stated that SRA and quicklime had a significant impact on concrete free-drying shrinkage reduction. It is assumed that a small amount of SRA (0.5–1.5% wt. of cement) in the concrete could significantly reduce concrete free-drying shrinkage to 28.3%. Similar experimental results are shown in study ,10,11. MWhile performing the free-drying shrinkage test, the changes in the mass of concrete specimens were observed, as shown in Test results showed that after 90 days of hardening, neither concrete composition lost more than 2% of the weight. The change in mass of the reference specimens after 9 days was 1.59%. The highest change in the weight of concrete was observed in the first days; as much as 34.0% of the total weight loss occurred during the first 3 days, and as much as 81.8% after 28 days of hardening. It is assumed that in the first days, the highest amount of free water evaporates from the concrete structure, resulting in the largest changes in the mass of the concrete.After noticing that most of the changes in length and weight occur during the first 28 days, it was decided to graph the relationship between these indicators. In the graph , all comThe relationship between the shrinkage and change in mass showed that as soon as shrinkage decreases, the change in mass increases. It is assumed that the more shrinkage deformations are reduced, the greater the change in mass can occur.The freeze–thaw resistance of concrete is important for concrete structures which are used in cold countries. The performance of concrete modified with different additives  and their combinations after 100 freezing-thawing cycles was investigated. All mixtures’ results were compared with the reference concrete. After 100 cycles, the samples were visually inspected a–k.Examination of freezing-thawing affected specimens showed a tendency for specimens containing 1.5% SRA to crack j,k or toDuring the analysis of the compressive strength results after 100 freeze-thaw cycles, it was observed that in nine of the eleven compositions, a decrease in the compressive strength occurs compared to the initial compressive strength after 28 days of hardening. The tests showed that the reference specimen (CNTRL) increased by 3.7% (47.2 MPa) from the initial compressive strength (45.5 MPa). POL3.0 specimens increased compressive strength by 10.6%. The hemp fiber (CNB3.0) led to the decrease in compressive strength by 8.8%. Specimens with 1.5% and 2.5% quicklime (Ca1.5 and Ca2.5) decreased compressive strength by 4.2% and 4.3%, respectively. Specimens with 0.5% SRA (SR0.5) compressive strength decreased by 6.7%. Moreover, specimens with hemp fiber, quicklime, and SRA (CNB3.0Ca2.5SR1.5) lost 12.2% of their initial strength. The highest decrease in compressive strength was obtained in specimens with 1.5% SRA, but POL3.0Ca2.5SR1.5). SR1.5, Ca1.5SR1.5, Ca2.5SR1.5 specimens lost 100% of compressive strength due to complete degradation of specimens. Specimens (POL3.0Ca2.5 SR1.5) lost 44.3% of their initial compressive strength. It is assumed that none of aforementioned additives increases concrete resistance to freezing-thawing cycles. High SRA (≥1.5% wt. of cement) content can cause concrete cracking and deterioration of its mechanical properties. In order to use concrete with SRA in places where freezing-thawing cycles occur, it is advisable to incorporate systems that increase freeze-thaw resistance, such as air entrainers or prefabricated air bubbles.By measuring the kinetics of water adsorption, concrete porosity parameters were determined. Total, open, and closed porosity is calculated by using the water adsorption test . The refCNB3.0 specimens adsorbed the highest amount of water 21.6%, and Ca2.5 specimens adsorbed the lowest amount of water 6.2% by comparing with the reference composition. The relationship between specimen densities and water adsorption was observed. It assumed that concrete with higher densities has the lowest water adsorption. Thus, the lower the density of the concrete specimens, the easier it is for the concrete to adsorb water, so it is necessary to increase the density of the concrete or the closed porosity to reduce the water adsorption.The types of concrete for porosity results are illustrated in The following conclusions were drawn from the research:The results of the experiment showed a significant reduction in concrete shrinkage when local quicklime powder is used as a shrinkage reducing additive. It was found that a small amount of local quicklime powder (>2.5% wt. of OPC) can reduce concrete shrinkage up to 21.5%. In addition, interactions with other shrinkage-reducing additives, such as SRAs based on organic compounds, can achieve even better shrinkage-reducing results. The combination of 1.5% SRA and 2.5% quicklime, which reduced shrinkage deformations up to 40%, was recommended. The drying shrinkage is closely related to physical and mechanical properties of concrete as well.3 polypropylene fiber. Meanwhile, the lowest strength had (POL3.0Ca2.5SR1.5) specimens with the 2.5% quicklime and 1.5% SRA addition. Moreover, this concrete had the highest fracture energy and residual strength of 1.9 MPa when a 3.5 mm crack appeared.The compressive strength test showed a strength decrease in all investigated compositions after 28 days of hardening. The highest decrease about 16.9% was obtained in composition (CNB3.0Ca2.5SR1.5) and the lowest 0.9% in composition (POL3.0). Flexural strength tests showed the highest strength increase (11.7%) in concrete with 3.0 kg/m3 hemp fiber reduced concrete workability, but increased air content, which is the main factor in the increase in closed porosity of hardened concrete. Compositions with 1.5% SRA were found to have a significant reduction in compressive strength after 100 freeze-thaw cycles. This observation is closely related to the morphology of hemp fibers.The parameters of water adsorption kinetics show that concretes with higher densities adsorb less water, while concretes with high closed porosity withstand higher amounts of freeze-thaw cycles. The water adsorption property of hemp fiber has been found to have a significant effect on the properties of concrete. Compared to the reference concrete, the use of 3.0 kg/m


Low-field nuclear magnetic resonance (NMR) and scanning electronic microscopy are used to investigate the change in the microstructure of concrete specimens under salt freeze–thaw cycles (FTCs). The results show the loss in compressive strength, mass, DEM, and NMR spectrum signal increased by 1.5–3 times, 3–5 times, 1.5–2.5 times, and 2–4 times, respectively, for concrete specimens under 50–100 FTCs in 6.8% composite salt solution, in comparison to fresh water. Apparent spalling, decreases in the DEM, and reductions in the compressive strength occur in concrete when increasing the number of salt FTCs. The number of internal cracks in the concrete structure increase under the combined action of salt crystallization, moisture absorption, and freeze–thaw. The changes in the internal microscopic pore volume in concrete structures exhibit the same trend with changes in the macro mechanical properties of concrete. The correlation coefficients between the changes in each peak in the NUR spectrum and the changes in the compressive strength of concrete specimens under FTCs in freshwater or low-concentration salt solutions are both larger than 0.7, calculated using the grey correlation degree method. Therefore, these changes could be used as a potential evaluation index for salt frozen damage to concrete structures.Herein, ordinary silicate concrete specimens are prepared to study the damage law of a cement-concrete material under the effects of salt erosion and a freeze–thaw environment. NaCl, NaHCO Freeze–thaw action significantly affects the durability of concrete; this action more severely damages the macroscopic properties of concrete when the environment experiences freezing and thawing over a long period . ResearcSalt environments significantly affect the durability of concrete structures, as salt erosion reduces their service life . The comLi  carried The mechanical properties of concrete structures, such as concrete dams and bridges, are greatly affected by freeze–thaw cycles ,15,16. S3. The coarse aggregates of cement concrete are graded crushed stone, with a particle size of 2–52 mm. The concrete mix proportion design is based on the code ‘specification for mix design of common concrete’ [Ordinary Portland cement 42.5 is used as the cement mortar material; its main parameters are listed in oncrete’ . The prooncrete’ ; the aveCubic specimens with dimensions of 100 mm × 100 mm × 100 mm are fabricated to test the compressive strength of concrete. Further, cuboid specimens with dimensions of 100 mm × 100 mm × 400 mm are made to test the DEM of concrete.+, SO42−, Cl−, and HCO3− in soil layers 30 cm away from the surface in western Jilin, China [2SO4 was 26.72 g/L, the mass of NaCl was 14.92 g/L, and the mass of NaHCO3 was 28.76 g/L. The amount of compound salt was the sum of each individual salt content.The tested concrete blocks were fabricated following Chinese Standard GB/T 50081-2019 . The cemn, China . Each si3 Powder X-ray powder diffraction machine is used to ascertain the composition of the material every 25 FTCs.The WAW-600 press machine is used to conduct the compressive strength experiment, the DT-20 ammunition instrument is used to test the DEM, MRE-60 low-field NMR is used to measure the pore characteristics of the material, the HC-RCTF quick tester for chloride ion contents is used to analyse the chloride concentration in each layer of the concrete material under the freeze–thaw action in a NaCl solution, the SU8010 scanning electron microscope is used to analyse the microstructural characteristics of the material, and the X’PertT2) of the pore size of the concrete structure, the sampling frequency was 250 kHz, the echo interval was 0.1 ms, the echo number was 12,000, and the signal ratio was greater than 100.The concrete specimens were analysed by XRD using X’Pert III equipment . The CuKα radiation was recorded in the 2θ range of 10°and 70°, using a single-channel detector. The radiation was collected at a step size of 0.013°, while the copper X-ray tube was operated at a 40 mA current intensity and a 40 kV voltage. The XRD analysis was performed on samples in a powder form, which were ground after the curing period. The NMR wave test was conducted using the MesoMR12-060H equipment , and the magnetic field intensity of the instrument was 0.3 ± 0.05 T (Tesla). The CPMG pulse sequence was applied to characterize the lateral relaxation time spectra , gel (C-S-H), calcium hydroxide (Ca(OH)2), and calcium sulphoaluminate hydrate (Aft/AFm). Each kind of salt gradually penetrates into the interior concrete and crystallizes to produce a larger crystal pressure with an increasing number of FTCs. There will be a greater ice pressure in concrete under the negative effect of salt, which will lead to more cracks being generated in the concrete’s internal structure, which leads to changes in the signal of the T2 spectrum and macroscopic mechanical properties of concrete. The intrusion of NaCl into the concrete leads to a loss of Ca(OH)2; the reaction of Na2SO4 and Ca(OH)2 will generate (CaSO4) and gradually generate ettringite (Aft). Calcite (CaCO3) and Na2CO3 will be generated after NaHCO3 infiltrates into concrete.From the XRD spectrum, it can be seen that the main components of the concrete material are silica 3 solution to the compressive strength and DEM of concrete is more severe than that of the two other kinds of salt solutions, and the damage to the internal structure is more severe than the surface erosion of concrete under FTCs in a NaCl solution.Based on the rapid freeze–thaw experiments in the salt solution based on the characteristics of saline soil in western Jilin, China, it can be seen that the damage caused by FTCs is more severe in the composite salt solution than that in freshwater. By comparing the effects of FTCs in the three kinds of single salt solutions comprising the composite salt, the damage of the NaHCO(2)When the concrete is subjected to freeze–thaw action in a salt solution, the moisture absorption of salt improves the pore saturation of concrete. The coupling effect of freshwater and crystallization pressure, which is generated when salt penetrates into the concrete, intensifies the damage to concrete. This damage makes the surface erosion and number of internal cracks gradually increase in the concrete; the increase in the middle pores and transition pores in the concrete is also more obvious.(3)T2 spectrum can be used as non-destructive testing metrics to evaluate the compressive strength damage of concrete after FTCs.From the correlation coefficients of concrete under freeze–thaw action in freshwater and salt solutions calculated by the grey correlation degree, it can be seen that the change characteristics of the DEM and pore variation are similar to the compressive strength of concrete. The characteristics of the DEM and (4)The durability research in this paper is mainly focused on the changes in the mechanical and physical properties of ordinary cement concrete blocks under rapid FTCs, and the performance variations in the air-entraining-agent-filled concrete, fibre-reinforced concrete, and ultra-high-strength concrete under the action of rapid FTCs in freshwater or salt solutions require further study. Further, the influence of the salt solution concentration on the related characteristics of concrete under rapid FTCs also needs to be further analysed.


Immunohistochemistry (IHC) is an alternative method of diagnosis but is not as reliable. Early studies of MET tyrosine kinase inhibitors (TKIs) demonstrated limited clinical benefit. However, newer selective MET TKIs, such as capmatinib and tepotinib, have improved efficacy. Both drugs have an acceptable safety profile with the most common treatment-related adverse event being peripheral edema. One of the most frequent resistance mechanisms to EGFR inhibition with osimertinib is MET amplification. There is interest in combining EGFR inhibition plus MET inhibition in an attempt to target this resistance mechanism. Additional ways of targeting MET alterations are currently under investigation, including the bi-specific antibody amivantamab. Additional research is needed to further understand resistance mechanisms to MET inhibition. There is limited research into the efficacy of immune checkpoint inhibition for MET-altered NSCLC, though some data suggests decreased efficacy compared with wild-type patients and increased toxicity associated with the combination of immunotherapy and MET TKIs. Future directions for research will include combination clinical trials and understanding rational combinations for MET alterations.The MET pathway can be activated by MET exon 14 skipping mutations, gene amplification, or overexpression. Mutations within this pathway carry a poor prognosis for patients with non-small cell lung cancer (NSCLC). MET exon 14 skipping mutations occur in 3-4% of patients with NSCLC, while MET amplifications are found in 1-6% of patients. The most effective method for detection of MET amplification is fluorescent  In the last decade, targeted cancer therapy has become a pillar in the management of non-small cell lung cancer (NSCLC). Genomic testing allows clinicians to identify oncogenic drivers that guide treatment decisions . The Natvia induction of VEGF. MET alterations include exon 14 skipping mutations, gene amplification, and protein overexpression  oncogene is a receptor tyrosine kinase primarily expressed in epithelial cells . MET sigpression . Each ofpression . MET exopression . MET amppression , 10.MET directed therapies have emerged in recent years as treatment options for patients with advanced NSCLC with MET exon 14 skipping mutations and amplification. These treatments include both tyrosine kinase inhibitors (TKIs) and antibodies, and can target MET and the MET ligand, hepatocyte growth factor (HGF) . The GEOMET exon 14 skipping mutations can occur through point mutations or genomic deletions that lead to a loss of exon 14. This increases protein stability by preventing ubiquitin-mediated degradation resulting in enhanced MET signaling and potential for malignancy , 13. TheMET amplification is a result of focal gene amplification which causes an increase in gene copy number (GCN). Approximately 1-6% of patients diagnosed with NSCLC have a MET amplification. In addition to its role in certain malignancies, it has also been identified as a mechanism of acquired resistance for EGFR TKIs .in-situ hybridization (FISH) from solid tissue biopsy is the gold standard for detection of MET amplification  is an alternative to FISH that is becoming increasingly more common for diagnosis of MET amplification and exon 14 skipping mutations. A caveat to NGS is that there is no standardized method of detection and some assays do not control for CEP7. Studies have shown a discrepancy between diagnosis of MET amplification using FISH versus NGS , 14, 16.via FISH and 1 via NGS. Two out of three of these same patients screened negative for MET amplification based on IHC results. In addition, 71 of 181 patients screened positive for a potential MET alteration based on MET IHC but only 1/71 had a confirmed MET amplification and 2/71 had a MET exon 14 skipping mutation (Immunohistochemistry (IHC) has been studied and used to detect MET overexpression. However, IHC is not a reliable predictor of MET alterations such as exon 14 skip mutations or amplification . In a smmutation .via RNA testing. However, 6 of those samples were not detected using DNA  that is shed from solid tumors . In addiRegardless of the method used, detecting MET alterations can be difficult due to both the wide array of variants that can lead to altered MET expression and lack of a standardized approach to diagnosis.via the solvent front residue, G1163, and are known as non-selective MET TKIs as this residue is not specific to MET. Type Ib inhibitors function independent of this residue and selectively bind to MET alone. Due to their selectivity, type Ib MET TKIs have superior anti-tumor activity and a more tolerable safety profile. Type II MET TKIs are also ATP-competitive inhibitors but instead bind to the inactive form of MET. Type III MET TKIs bind allosterically outside of the ATP domain  with median PFS of only 4.4 months (95% CI 3.0-5.8) . SimilarCapmatinib was FDA-approved for treatment of NSCLC with MET exon 14 skipping mutations in 2020. This was based on data from the GEOMETRY Mono-1 study, a phase II clinical trial. The study enrolled 364 patients with confirmed MET exon 14 skipping mutations or MET amplification. Patients were further stratified based on prior treatment history. Among patients with MET exon 14 skipping mutations, 69 received prior therapy and had an ORR of 41% (95% CI 29-53) and median PFS of 5.4 months (95% CI 4.2-7.0). In contrast, 28 treatment-naïve patients had an ORR of 68% (95% CI 48-84) and median PFS of 12.4 months (95% CI 8.2-NE). The time to respond to capmatinib was rapid for both groups, as short as first tumor evaluation at 6 weeks. Results suggested an increased benefit in the treatment naïve population .Patients with MET-amplified NSCLC had limited response to capmatinib. The trial closed early for futility in patients with MET amplification with GCN <10. While tumor response was seen for patients with GCN ≥ 10, this still did not meet the threshold for clinical relevance  .Capmatinib had an acceptable safety profile. TRAEs occurred in 88% of patients who received treatment, with peripheral edema seen in 50% of patients. Grade 3 or higher adverse events occurred in 67% of participants, and again peripheral edema was the most common high-grade event. Serious TRAEs were seen in 13% of participants and 11% discontinued treatment as a result , 33.The phase II VISION trial led to FDA approval of tepotinib in 2021 as a second-line therapy for patients with MET exon skipping NSCLC. A total of 152 patients with MET exon 14 skipping mutations were enrolled in the study and received treatment. There was an ORR of 46% (95% CI 36-57) based on independent review, and median PFS was 8.5 months (95% CI 6.7-11). There was no significant difference in response for patients who had received prior lines of treatment from those who had not . ResponsTRAEs occurred in 89% of patients. Peripheral edema was the most common adverse effect, occurred in 63% of patients, lead to dose reduction in 16% of patients, dose interruption in 18%, and discontinuation in 5%. Twenty-eight percent of participants experienced a grade 3 or higher adverse event. The most common high-grade event (7%) was peripheral edema, followed by increased amylase and lipase. Serious TRAEs were reported in 15% of patients and 11% discontinued treatment , 34, 35.A sub-group analysis of 23 patients with MET exon 14 skipping mutations and brain metastases demonstrated a robust treatment response with an ORR of 47.8% (95% CI 26.8-69.4) and median DOR of 9.5 months (95% CI 5.5-NE). There were 15 patients evaluated using Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) criteria, 12 received prior chemotherapy. 7 patients had measurable disease per RANO-BM and 8 had non-enhancing, non-target lesions. 9 had a partial response (PR), 3 with stable disease (SD), and 3 with progressive disease (PD) .The efficacy and safety of tepotinib in an elderly population over the age of 75 with MET exon 14-altered NSCLC was further investigated in an additional group of patients and was consistent with the findings from the VISION trial  . PeripheResults from the VISION trial in patients with MET-amplified NSCLC were analyzed separately. MET amplification was defined as GCN ≥2.5. A total of 24 patients were enrolled in the study with an ORR of 41.7% (95% CI 22.1-63.4) and median PFS of 4.2 months (95% CI 1.4-NE). Sixteen patients reported TRAEs of any grade and 7 of those patients were grade 3 or higher. Peripheral edema was again the most common adverse event and was reported in 37.5% of patients Table 1.Savolitinib was approved in China for conditional use in NSCLC with MET exon 14 skipping mutations following a multi-center phase II trial. The study enrolled 70 patients with confirmed MET exon 14 skipping mutations; 36% had pulmonary sarcomatoid carcinoma. There was an ORR of 49.2% (95% CI 31.1-55.3) in the tumor response evaluable set with a median PFS of 6.9 months and median OS of 14 months . Forty-sCabozantinib is another non-selective MET TKI that targets VEGFR1-3, RET, TIE2, FLT-3, KIT, and MET. It is currently FDA-approved for treatment of medullary thyroid cancer, renal cell carcinoma, and hepatocellular carcinoma. In a phase II trial, patients with advanced NSCLC with wild-type EGFR were randomized to receive cabozantinib alone, erlotinib alone, or erlotinib with cabozantinib. The study showed improved PFS in the cabozantinib alone group  and the cabozantinib and erlotinib combination cohort  compared to erlotinib alone   . More daFor information regarding additional Type II MET TKIs including merestinib, foretinib, and glesatinib and the Type III MET TKI, tivantinib, please see In addition to MET TKIs, there are several antibodies targeting MET that have been studied or are in development for treatment of NSCLC. Amivantamab is a bispecific antibody targeting EGFR and MET. It was first presented in the phase I CRYSALIS study, which included a population of NSCLC patients with EGFR exon 20 insertion. There was an ORR of 40% (95% CI 29-51) and median PFS of 8.3 months (95% CI 6.5-10.9). The most common adverse events were rash and infusion reactions, and the most common severe adverse event was hypokalemia (5%) . UpdatedEarly data from the phase II CHRYSALIS-2 trial was also presented at the 2022 ASCO meeting in which amivantamab was given in combination with the EGFR TKI, lazertinib, for patients with NSCLC who progressed on platinum-based chemotherapy and osimertinib. There were 162 patients who received treatment with an ORR of 33% and clinical benefit rate of 57% with median DOR of 9.6 months . The ongpost hoc analysis revealed that for 24 patients with markedly high MET expression there was a significant improvement in median PFS of 15.3 months in the combination group , telisotuzumab vedotin, was developed. The ADC consists of a c-MET antibody linked to a microtubule inhibitor and was given FDA breakthrough therapy designation for EGFR wild-type NSCLC following initial data from the ongoing phase II LUMINOSITY trial. Tumors were tested for c-MET overexpression using IHC and subdivided into intermediate or high c-MET expression groups. Of the 136 patients who received treatment so far, there was an ORR of 52.2% in the c-MET high, EGFR wild-type group and 24.1% in the c-MET intermediate, EGFR wild-type group. Peripheral neuropathy, nausea, and low albumin levels were the most common TRAEs .One other MET antibody under investigation is Sym015, which is made up of a mixture of 2 humanized antibodies .The anti>50%) or tumor mutational burden in predicting response to immunotherapy in this group of patients  in patients with MET-altered NSCLC. Several studies have demonstrated modest efficacy , 50. Thipatients , 51.Interestingly, one retrospective, multicenter study demonstrated an improved response to ICI therapy. Thirty patients with a MET mutation were evaluated and received either pembrolizumab or nivolumab. There was an ORR of 35.7% and median PFS of 4.9 months 95% CI 2.3-NE) . NCCN gu.3-NE . Np=0.001) (p=0.004). A similar improvement in OS was seen with GCN <10 treated with ICI versus chemotherapy . In contrast, OS was not statistically improved for patients with MET exon 14 skipping mutations   . While Mp=0.147) . These fOne reason immunotherapy may have limited efficacy in MET-altered NSCLC is through inhibition of stimulator of interferon gene (STING) signaling. The STING pathway promotes interferon (IFN) response and is integral in the recruitment of T-cells and NK-cells . A retroThe combination of a MET TKI with an ICI could potentially overcome resistance to immunotherapy. However, there is concern for increased toxicity with combination therapy. One phase II trial of NSCLC with high tumor PD-L1 expression (≥50%) randomized treatment-naïve patients 2:1 to receive combination pembrolizumab and capmatinib or pembrolizumab alone. The trial was terminated early due to toxicity concerns with combination therapy. At data cutoff, 51 patients were enrolled in the combination arm and 25 in the pembrolizumab-alone arm. Nineteen out of fifty-one patients (37.3%) in the combination arm discontinued treatment with 4 suspected deaths. Seven patients (28%) discontinued treatment in the single therapy arm . FurtherEGFR TKIs have been highly successful in the treatment of EGFR-mutant NSCLC. However, development of acquired resistance is common, and limits the long-term efficacy of this class of drugs. Approximately 60% of resistance to first generation EGFR TKIs is due to the T790M mutation which inhibits binding of TKIs to the ATP binding site of EGFR. Third generation EGFR TKIs such as osimertinib were subsequently developed to overcome common EGFR TKI resistance mechanisms such as the T790M mutation. MET amplification is another important mechanism of acquired resistance to EGFR TKIs that activates oncogenic signaling cascades downstream of EGFR through a bypass pathway –59. It oSeveral trials have attempted to overcome resistance through combination therapy with MET TKIs. The INSIGHT study is a phase Ib/II trial that investigated the combination of tepotinib and gefitinib in patients with EGFR-mutant, T790M negative NSCLC with acquired resistance to EGFR TKI therapy compared to chemotherapy. While survival outcomes were similar overall for tepotinib and gefitinib compared to chemotherapy, sub-group analysis demonstrated a significant improvement in PFS and OS for patients with MET amplification treated with combination therapy  . A notabAdditional studies that utilized combination MET and EGFR TKIs to overcome MET-amplified EGFR TKI resistance include a phase Ib/II trial evaluating capmatinib and gefitinib and the phase Ib TATTON trial which included osimertinib in combination with savolitinib. Both showed similarly promising results to INSIGHT Table 3 via activation of oncogenic signaling cascades downstream from MET such as the MAPK and PI3K/AKT pathways. This can be mediated by mutations and amplifications in EGFR, KRAS, HER3, and BRAF (While MET TKIs have demonstrated clinical benefit and tolerable toxicity, the ability to diagnose and sequence MET alterations remains a challenge and there are currently no standardized methods to confirm MET alterations. In addition, as with all TKIs, duration of response can be limited by resistance. There are several proposed mechanisms of on-target and off-target resistance to MET TKIs. On-target mutations can affect drug-receptor binding and ATP inhibition , 64. Sevand BRAF , 64. Swiand BRAF . While tThere is an emerging role for combination therapy with MET and EGFR TKIs in EGFR-mutant NSCLC. Further research is needed to understand additional combination therapies in MET-altered NSCLC, including MET TKIs and ICIs. Several new agents targeting MET alterations are currently under investigation including the bi-specific antibody amivantamab. While not yet studied, such agents may be combined or used in place of MET TKIs to delay or prevent resistance.Treatment of NSCLC has significantly changed over the last decade with the rise of genetic testing and targeted cancer therapy. Activation of the MET pathway is an important oncogenic driver for many patients with NSCLC and has proven to be an effective target for therapy. The development of MET TKIs and, in particular, the selective MET TKIs tepotinib, capmatinib, and savolitinib, has altered the landscape of cancer treatment for an older population of patients who previously had limited treatment options outside of chemotherapy. The more recent emergence of MET antibodies including the bispecific antibody, amivantamab, is expanding upon available treatment options and is currently being studied as potential first-line therapy for EGFR-mutant NSCLC.All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.CB reports the following disclosures: Advisory Board: AstraZeneca, BMS, Genentech, Jazz, JNJ, Novartis, Pfizer, Seattle Genetics, Takeda; Consulting Fee: Axiom Healthcare, Cardinal Health, Curio Science, CVS, OncLive. Targeted Oncology; Contracted Research: BMS; Speakers Bureau: Merck.The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The aim of this study was to investigate the use of streptococcal antigen tests and antibiotic prescription in general practice in Norway in relation to the national guidelines for sore throat.This study was based on a web-based survey.Norwegian general practice.4700 members of the Norwegian College of General Practice received the survey by E-mail.General practitioner (GP) adherence to national guidelines.not perform the test at moderate infection. Phenoxymethylpenicillin was recommended by 95% of the GPs.In total, 807 GPs responded and were included in the study. According to the guidelines, 20% and 30% of the GPs would perform unnecessary streptococcal antigen testing when presented with mild and severe infections respectively, while 52% would Norwegian guidelines for diagnosis and treatment of throat infections include the use of Centor criteria as a clinical tool to limit the unnecessary use of antibiotics. In this web-based survey, we investigated the use of streptococcal antigen tests and antibiotic prescription in general practice in relation to the national guidelines.•Streptococcal antigen tests were not always performed according to Norwegian guidelines, causing inappropriate antibiotic prescribing.•National guidelines were followed in the choice of antibiotics for sore throat.In this survey of self-selected GPs, we identified some non-adherence to National guidelines for streptococcal antigen testing and antibiotic prescribing. However, when antibiotic treatment was offered, the correct antibiotics were prescribed. Streptococcus (GAS) accounts for approximately 5–40% of the cases across populations [In Norway, approximately 84% of all antibiotics are prescribed in primary health care and approximately half are prescribed to treat respiratory tract infections . Sore thulations . Most caulations . Inapproulations . The Cenulations .‘Choosing wisely’ is a clinician-led campaign aiming to avoid the unnecessary use of medical procedures, diagnostic tests, and treatments. The goal is to reduce adverse effects associated with unnecessary treatment and thereby improve patient safety, and to omit healthcare costs associated with tests and treatments that provide no benefit or lacks clinical indication. The campaign was launched in the USA in 2012 and has since then been implemented in more than 20 countries, including Norway . In NorwThe Norwegian Organization for Quality Improvement of Laboratory Examinations (Noklus)  is a natSupplementary material (1). The cases fulfilled the four Centor criteria to different degrees. The criteria are (i) fever >38.5 °C, (ii) swollen and tender anterior cervical lymph nodes, (iii) tonsillar exudate and (iv) absence of cough. The survey was open for invited GPs only and was conducted between September 17 and October 17, 2020. After being presented to each case, the participants were asked if they would perform a streptococcal antigen test and whether they would prescribe antibiotics. In cases 1 and 2, responders that would recommend antibiotic treatment were presented to the follow-up questions: ‘Which antibiotic treatment would you offer?’ and ‘For how many days would you prescribe antibiotic therapy?’. Additionally, in cases 1 and 2, patient temperatures were measured in the armpit. Temperatures measured axillary are lower than temperatures measured in the ear, under the tongue or rectal, which means that the patient in case 2 probably had a fever >38.5 °C.A web-based survey describing three cases of sore throat  was distThe survey was designed as a ‘mini course’; after each question, the respondents were provided with correct/preferred answers with references, but without the ability to correct their initial response. For educational purposes, the survey remains available on Noklus webpage . FurtherDuring the data collection period, 905 GPs responded to the survey . Of thesWould you offer antibiotic treatment?’, 634 (79%) GPs recommended no antibiotic therapy, 10 GPs recommended antibiotic treatment, whereas 163 (95%) of the GPs who recommended antigen tests would treat with antibiotics only if the test was positive. Overall, 628 (79%) GPs, reported that they would neither recommend streptococcal antigen testing nor antibiotic treatment.Case 1 described mild infection with an absence of cough as the only Centor criterium fulfilled. Of the 807 responding GPs, 171 (21%) answered they would perform streptococcal antigen testing . When asCase 2 described moderate infection with fever (38.2 °C in the armpit) and with swollen and tender anterior cervical lymph nodes. Of the 799 responses collected, 373 (48%) GPs indicated that they would perform a streptococcal antigen test. Antibiotic therapy was recommended by 9 (1%) GPs, whereas 351 (45%) indicated they would recommend treatment only if the strep test was positive. A total of 412 (53%) GPs responded that they would not offer any antibiotic treatment.Case 3 presented all four Centor criteria. 243 (32%) of the 749 responding GPs answered they would perform a streptococcal antigen test. Subsequently, antibiotic treatment was recommended by 631 (85%) GPs while 114 (15%) GPs would offer treatment only if the antigen test was positive. In total, 505 (85%) GPs would offer antibiotics without any prior antigen testing.p = 0.002 for trend). GPs with more than 10 years in practice, for instance, were somewhat less likely to offer antibiotics according to guidelines than colleagues with 0–1 years in practice (OR 0.64 95% CI 0.485–0.845).In cases 1 and 2, there were no associations between ‘Years in practice’ or ‘Number of patients on the list’ and reporting that they would perform a streptococcal antigen test or offer antibiotics. In case 3, however, we observed a trend that GPs were less likely to offer antibiotics according to guidelines with increasing year in practice  or severe infection (four Centor criteria), most of the participating GPs responded in accordance with the guidelines regarding the use of streptococcal antigen tests and prescription of antibiotics. Yet nearly 20% of the GPs would perform antigen testing at mild infection in case 1 which is considered unnecessary since the risk of GAS infection is low. As a consequential error, most of these GPs then indicate they would prescribe antibiotics if the antigen test was positive. Carriage of GAS is common, especially among children . Thus, anot perform a streptococcal antigen test at moderate infection as presented in case 2 (two Centor Criteria present), a setting where a patient could benefit from performing the test. Centor Criteria were developed for adults, and it has been shown that these criteria are not a good tool to assess the probability of GAS infections in children [not perform streptococcal antigen testing of the nine-year-old patient described in case 2.Furthermore, 243 (30%) of the GPs indicate that they would perform streptococcal antigen testing at severe infection in case 3, which are considered unnecessary according to the Norwegian guidelines. Recommendations regarding the use of Streptococcal antigen tests differ between countries. Swedish guidelines recommend testing when three or more Centor criteria are present, and patients are treated only when tests are positive , whereaschildren . TherefoFurther, at moderate infection nearly all the GPs (98%) recommended antibiotic treatment only if the antigen test were positive or not at all. In this setting, antibiotic treatment could be discussed in consultation with the patient to limit the use of antibiotics. Previous studies have suggested that GPs with more years in practice prescribe antibiotics more often than GPs with less years in practice ,17. We dIn our survey, most of the GPs (95%) would prescribe beta-lactamase-sensitive penicillin. This is in accordance with guidelines, which recommend phenoxymethylpenicillin as first-line treatment for most respiratory tract infections when antibiotic therapy is indicated. Approximately 4–5% of the GPs indicated that they would offer broad-spectrum antibiotics. Macrolides were also suggested by a few GPs. Treatment of upper respiratory tract infections with second-choice antibiotics is almost always unnecessary. Hence, treatment with broad-spectrum antibiotics in cases 1 and 2 would not be in accordance with guidelines. These findings are consistent with previous reports showing that macrolides and penicillin with extended-spectrum are used more often than recommended ,19. The At the time of survey completion, the recommended treatment regimen in Norway for adults was 660 mg phenoxymethylpenicillin four times daily for 10 days. However, in the recently revised guidelines, the recommended duration of treatment is reduced from 10 to 5 days ,22. A SwFor several years there has been a focus on reducing antibiotic prescribing as well as offering narrow-spectrum antibiotics rather than broad-spectrum antibiotics, and this may have contributed to the high guideline adherence to first-line treatment we found in this survey. In 2015 the Norwegian government launched a national strategy to reduce antibiotic consumption . VariousIn our survey, we however observed less adherence to the national guidelines when it came to the use of streptococcal antigen tests. This is despite previously mentioned measures focusing on appropriate testing. At severe infection, 30% reported that they would perform a test (not according to guidelines), and one could speculate if some GPs perhaps are relying on their clinical experience instead of following the guidelines rigorously. Also, in general practice there is patient expectations to consider. The extensive use of rapid tests in Norwegian primary care can lead patients with a sore throat to expect that a streptococcal antigen test must be taken, which in turn can influence the doctor’s choice.not perform a test (not according to guidelines). It is possible that some GPs did not perform a streptococcal antigen test because the patient described in this case was a child with typical cold symptoms. Moreover, insight into reasons for non-adherence to guidelines was not within the scope of this study; however, in general practice, great degree of confidence in own clinical judgment, time pressure, patient expectations, and difficulties in remembering the guidelines have been reported as reasons for not following guidelines [At moderate infection, 52% of the GPs would idelines .In Norway, prescriptions of antibiotics to treat respiratory tract infections are frequent even though most cases of sore throat will resolve without treatment ,3. NatioClick here for additional data file.


Mesenchymal epithelial transition factor (MET) gene encodes a receptor tyrosine kinase with pleiotropic functions in cancer. MET exon 14 skipping alterations and high-level MET amplification are oncogenic and targetable genetic changes in patients with non-small-cell lung cancer (NSCLC). Resistance to tyrosine kinase inhibitors (TKIs) has been a major challenge for targeted therapies that impairs their clinical efficacies.The MET tyrosine kinase domain (TKD) mutations . Baseline and paired TKI treatment samples were analyzed by targeted next-generation sequencing.Eighty-six NSCLC patients were categorized into three cohorts based on the time of detecting MET TKD mutations were highly prevalent in METex14-positive NSCLC patients after MET-TKI treatment, including L1195V, D1228N/H/Y/E, Y1230C/H/N/S, and a double-mutant within codons D1228 and M1229. Missense mutations in MET TKD were also identified at baseline and in post-EGFR-TKI treatment samples, which showed different distribution patterns than those in post-MET-TKI treatment samples. Remarkably, H1094Y and L1195F, absent from MET-TKI-treated patients, were the predominant type of MET TKD mutations in patients after EGFR-TKI treatment. D1228H, which was not found in treatment-naïve patients, also accounted for 14.3% of all MET TKD mutations in EGFR-TKI-treated samples. Two patients with baseline EGFR-sensitizing mutations who acquired MET-V1092I or MET-H1094Y after first-line EGFR-TKI treatment experienced an overall improvement in their clinical symptoms, followed by targeted therapy with MET-TKIs.MET TKD mutations were identified in both baseline and patients treated with TKIs. MET-H1094Y might play an oncogenic role in NSCLC and may confer acquired resistance to EGFR-TKIs. Preliminary data indicates that EGFR-mutated NSCLC patients who acquired MET-V1092I or MET-H1094Y may benefit from combinatorial therapy with EGFR-TKI and MET-TKI, providing insights into personalized medical treatment.The online version contains supplementary material available at 10.1186/s12931-023-02329-1. Lung cancer is the leading cause of cancer-related mortality worldwide, and non-small-cell lung cancer (NSCLC) represents the major histological subtypes of the disease . A majorMET exon 14 skipping alterations (METex14), resulting in decreased MET turnover and extended oncogenic downstream signaling pathways [MET (METamp) may also rarely occur as a primary oncogenic driver and is more frequently identified in the context of acquired bypass resistance to EGFR-TKIs [Enormous efforts have been made to identify activating mutations, particularly those involved in cancer initiation and drug resistance. Approximately 3% of NSCLC patients harbor pathways , 3. The GFR-TKIs . On the GFR-TKIs .METex14 or METamp, additional MET activating mutations have been clinically documented and preclinically characterized to confer resistance to type I MET inhibitors  while being sensitive to type II MET inhibitors  [METex14-altered NSCLC by disrupting drug binding. Recent studies have also shown that mutations in L1195 and F1200 residues confer acquired resistance to type II MET-TKIs [MET TKD mutations that might contribute to acquired resistance to TKIs is required.In NSCLC patients harboring estinib) –10. In pMET TKD mutations. Our study revealed a broad spectrum of MET TKD mutations and provided insights into potential acquired resistance mechanisms to TKIs.In this study, we assessed the targeted sequencing data of 86 NSCLC patients harboring MET TKD mutation-positive patients whose samples were collected at all participating hospitals. The study was approved by the Medical Ethics Committee of Nanjing Geneseeq Medical Laboratory (NSJB-MEC-2023-01). Written consent was obtained from each patient before sample collection. Qualified samples were analyzed by targeted next-generation sequencing using targeted gene panels in a CLIA-certified and CAP-accredited clinical testing laboratory . Formalin-fixed paraffin-embedded (FFPE) tissue samples were confirmed by pathologists from the centralized clinical testing center before genetic testing. Liquid biopsies were shipped within 48 h of sample collection to the central testing laboratory for cell-free DNA (cfDNA) extraction and the following tests. Clinical characteristics and treatment history were extracted from medical records.The extensive database search identified 54,752 NSCLC patients whose tumor specimens and liquid biopsies, including plasma, cardiomyocyte fluid, pleural effusion, and cerebrospinal fluid, were analyzed by targeted NGS between June 2015 and November 2022 at Nanjing Geneseeq Technology Inc. This study included 138 DNA extraction was carried out following standard protocols as previously described , 14. Spehttps://github.com/lh3/bwa/tree/master/bwakit). Genome Analysis Toolkit  was employed to perform local realignment around the indels and base quality score recalibration. Picard was used to remove duplicates generated during sample preparation. VarScan2 was applied to detect single-nucleotide variations (SNVs) and insertion/deletion mutations. SNVs were filtered out if the variant allele frequency (VAF) was less than 1% for tumor tissue and 0.3% for liquid biopsy samples. Common SNVs were excluded if they were present in > 1% population in the 1000 Genomes Project or the Exome Aggregation Consortium 65,000 exomes database. The resulting mutation list was further filtered by an in-house list of recurrent artifacts based on a normal pool of whole blood samples. Parallel sequencing of matched white blood cells (control) from each patient was performed to remove sequencing artifacts, germline variants, and clonal hematopoiesis.Sequencing data were first demultiplexed and subjected to FASTQ file quality control using Trimmomatic . QualifiP value of less than 0.05 was considered significant for all tests unless indicated otherwise . All statistical analyses were performed in R (version 4.1.3).Two-proportional t-test was used to determine whether the two proportions were different from each other. Wilcoxon signed-rank test was used to compare if there were differences between paired observations. A two-sided MET TKD mutations. In particular, MET TKD mutations were identified in 32 treatment-naïve NSCLC patients (cohort 1), 41 MET-TKI-treated patients (cohort 2), and 13 EGFR-TKI-treated patients (cohort 3). Notably, 20 patients in cohort 2 were pretreated with EGFR-TKIs before the onset of MET-TKI treatment. The clinical characteristics of these 86 patients are summarized in Table A total of 138 NSCLC patients harboring somatic mutations in the MET TKD assessed by targeted NGS were identified from an extensive database search , including H1094Y/D, L1195F/V, D1228N/Y and Y1230C/H , METamp , and METex14 , were identified in these baseline patients. Additionally, one patient exhibited an ALK rearrangement, another known oncogenic driver in NSCLC. By comparing the mutational profiles of these patients, we found that 37.5% of baseline MET TKD mutation-positive patients (12/32) harbor at least one known oncogenic driver alteration. Of those 20 mutually exclusive MET TKD mutations found at baseline, H1094Y was detected in 8 patients, followed by L1195F and D1228N in 5 and 3 individuals, respectively , D1228H (42%), Y1230H (20%), Y1230C (15%), D1228Y (12%), and L1195V (10%). It is worth noting that a double-mutant within codons D1228 and M1229 (MET-D1228_M1229delinsFL) was identified in the post-treatment sample of P124. We also observed that V1092I and H1094Y mutations initially identified in samples after first-line EGFR-TKI treatment of patients 24 (P24) and 26 (P26) were no longer detectable after MET-TKI treatment , L1195F (23%), D1228N (23%), D1228H (15%), D1228Y (8%), and L1195V (8%)  and PIK3CA-D1045N (VAF 1.64%), the VAF of MET-1094Y was significantly higher (VAF 9.9%). In addition, PIK3CA-D1045N (VAF 1.64%) identified in the pre-EGFR-TKI treatment sample has not been annotated based on OncoKB (https://www.oncokb.org/). Despite a likely oncogenic role of PIK3CA-C604R in patient 36, this mutation was identified in pre-EGFR-TKI treatment samples of the same patient. While the VAF of EGFR mutations dropped after EGFR-TKI treatment, the opposite was observed in MET TKD mutations , suggesting a potential acquired resistance mechanism to EGFR-TKIs. In contrast, D1228N and Y1230C/H are more likely associated with acquired resistance to MET-TKIs in NSCLC.Comparing the two TKI-treated groups, we noticed that H1094Y and L1195F mutations, while being the predominant type of EGFR-sensitizing mutations has achieved great success. However, disease remission remains a major obstacle due to acquired resistance. Here, we demonstrate that co-targeting both EGFR and MET might be a promising treatment regimen for patients who become resistant to EGFR-TKIs due to acquired MET TKD mutations.Precision medicine using EGFR-TKIs on NSCLC patients harboring MET-V1092I mutation (VAF 27.7%), the patient was treated with cabozantinib and capmatinib, followed by two cycles of chemotherapy. Targeted sequencing identified MET-D1228N (VAF 2.8%) as well as PI3KCA and BRAF mutations. Treatment was subsequently switched to combinatorial therapy with capmatinib and dacomitinib, and the patient experienced an overall improvement in the clinical symptoms until the symptoms worsened again after three months of treatment. A similar attempt was made in P26, where treating the patient with gefitinib plus crizotinib effectively overcame the MET-H1094Y mutation . The α and β chains encompass the remainder of the extracellular domain, the juxtamembrane domain, and the kinase domain. The intracellular part of MET contains a juxtamembrane region responsible for signal regulation and receptor degradation, a catalytic region with enzyme activity, and a C-terminal region acting as a docking site for adaptor proteins. b The binding of HGF to MET leads to receptor dimerization and phosphorylation of tyrosine residues in the kinase domain and autophosphorylation of the C-terminal docking sites, which activates downstream oncogenic signaling pathways, such as RAS/MAPK, PI3K/AKT, and STAT3. AKT, protein kinase B; MET, MET proto-oncogene; PI3K, phosphoinositide 3-kinase; RAS, rat sarcoma virus; MAPK, mitogen-activated protein kinase; STAT, signal transducer and activator of transcription proteins.Additional file 2: Figure S2. Variant allele frequency and copy number change in three patient cohorts. a Variant allele frequency (VAF) of EGFR and MET TKD mutations in baseline patients. b The copy number of MET amplification before and after MET-TKI treatment. c VAF of MET exon 14 skipping alterations (METex14) before and after MET-TKI treatment. d VAF of EGFR and MET TKD mutations in patients before and after EGFR-TKI treatment.