the introduction of the immunomodulatory drug lenalidomide has revolutionized the treatment of patients with myelodysplastic syndromes ( mds ) and deletion of the long arm of chromosome 5 . treatment with lenalidomide results in transfusion independence in the majority of patients , but some questions remain unresolved , among them the duration of treatment . moreover , a number of unexpected long - term remissions in patients who stopped lenalidomide for various reasons have been observed . we report the case of a 60-year - old caucasian male with deletion of the long arm of chromosome 5 and international prognostic scoring system ( ipss)-defined low - risk mds who was treated with lenalidomide , achieving complete cytogenetic remission and erythroid response . after tapering off and interrupting the treatment , the patient relapsed and showed a new response by lenalidomide retreatment . six years after the initial treatment , we registered a durable erythroid long - term response and good tolerance , but there was no evidence of a very profound cytogenetic response compared to using lenalidomide as a first - line treatment . cytogenetic and fluorescence in situ hybridization together with hemoglobin level , mean corpuscular volume ( mcv ) and vitamin b12 level helped us to monitor the patient response ; during the various phases of lenalidomide treatment , mcv and vitamin b12 normalization correlated with good response . lenalidomide interruption and rechallenge in some 5q mds patients , with low risk according to the ipss , is safe and feasible but does not result in a profound cytogenetic response . myelodysplastic syndromes ( mds ) are clonal bone marrow disorders characterized by ineffective bone marrow hematopoiesis , peripheral blood cytopenias and risk of transformation to acute myeloid leukemia ( aml ) . patients are stratified according to the international prognostic scoring system ( ipss ) into low- , intermediate-1- , intermediate-2- and high - risk categories . among cytogenetic abnormalities , partial or complete deletion of the long arm of chromosome 5 [ del(5q ) ] is the most common cytogenetic abnormality found in mds patients , occurring in 1015% of all de novo mds patients [ 2 , 3 ] and in up to 30% of cases with abnormal karyotype . the prognosis of mds cases with del(5q ) worsens with additional cytogenetic changes and increase in blast percentages . treatment with the immunomodulatory drug lenalidomide has set a new standard for the management of low / intermediate-1-risk mds with 5q in transfusion - dependent patients . lenalidomide suppresses the growth of mds progenitors harboring 5q , giving rise to a high frequency of transfusion independence ( ti ) and cytogenetic response and promotes erythroid lineage competence and colony - forming capacity . lenalidomide may restore transcriptional response to endogenous erythropoietin in mds progenitors , suggesting that lenalidomide enhances cellular responsiveness to erythropoietin stimulation ; moreover , p53 expression in erythroid precursors decreased in lenalidomide responders but is upregulated upon the emergence of resistance to lenalidomide . the current treatment recommendation is to treat 5q with lenalidomide until relapse or transfusion dependence or progressive disease . consequences of the long - term effects of continuous immunomodulation with lenalidomide are unknown , and the question whether interruption of lenalidomide treatment is beneficial for patients in remission has never been formally addressed . we herein report a patient with mds with isolated 5q deletion and ipss - defined low - risk mds , who was treated with lenalidomide , achieving complete cytogenetic remission and erythroid response , and who after tapering off and interrupting the treatment relapsed . a new response was observed after re - exposure to lenalidomide , showing durable erythroid long - term response and good tolerance , but cytogenetic response was not very profound . a 60-year - old caucasian male was first seen for the evaluation of macrocytic anemia , weakness and easy fatigue . laboratory analyses confirmed the macrocytic anemia : hemoglobin ( hb ) 10.6 g / dl ; mean corpuscular volume ( mcv ) 109 fl with a normal reticulocyte count ; white blood cell count ( wbc ) was 3.34  10/l ; absolute neutrophil count ( anc ) was 1.87  10/l , and platelet count was 215  10/l . bone marrow aspirate and biopsy were performed revealing hypoplastic bone marrow with dyserythropoiesis , no ring sideroblasts were present , and micromegakaryocytes with single eccentric nuclei were also observed . cytogenetic analysis showed 5q with no other abnormalities ; at least 10 metaphases and whenever possible 2025 metaphases were analyzed by the classical cytogenetic method . the karyotype was written as 46 , xy , del(5)(q31 ) . a diagnosis of mds with isolated 5q iu / l and the patient was transfusion - independent ; therefore , we observed him periodically . after 11 months , he showed a decline in the hb level : hb was 9.8 g / dl , mcv 112 fl and the serum erythropoietin level was less than 200 we then treated the patient with 40,000 iu of erythropoietin  biweekly for 6 months . despite erythropoietin after 7 months of this treatment , hb was 7.9 g / dl , mcv was 110 fl , vitamin b12 was 930 pg / ml ( range 191663 ) , the bone marrow showed an increased dyserythropoiesis , and the fluorescence in situ hybridization ( fish ) analysis , using lsi5q31 ( egr1)/d5s23 , d5s721 probe ( abbott , molecular inc . , usa ) on 200 interphase nuclei , permitted to detect a higher percentage of cells with 5q since the diagnosis ( 65 vs. 45% ) . the patient refused transfusion and lenalidomide was initiated at a dose of 10 mg / day for 21 days every 4 weeks , together with aspirin as thromboprophylaxis ( anc was 1.6  10/l and platelet count 301  10/l ) . weekly blood controls showed grade 3 neutropenia and growth factor ( g - csf ) support was initiated biweekly from the second cycle of treatment to the fifth . after 5 cycles of standard treatment , the patient obtained complete hematological and cytogenetic remission : hb was 12.6 g / dl , mcv 98 fl , vitamin b12 600 pg / ml , wbc 4.4  10/l , anc 3.3  10/l , and platelet count was 135  10/l . we suspended the growth factor support and tapered off the dose of lenalidomide ( initially 5 mg for 21 days every 4 weeks for 3 cycles and subsequently 5 mg every other day for 21 days every 4 weeks for 6 cycles ) . then we treated him with 5 mg biweekly for 3 weeks of every 28-day cycle for 12 cycles , remaining transfusion independent and in complete hematological and cytogenetic remission ( fig . 1 ; table 1 ) , with a range of platelet count between 149 and 128  10/l . after 1 year of this schedule , the patient had a cytogenetic relapse with 2/10 metaphases and 18% interphase nuclei showing a 5q ( fig . 1 ) , but he remained transfusion independent ( hb 13.9 g / dl , mcv 100 fl , platelet count 128  10/l , wbc 3.5  10/l , anc 1.09  10/l and vitamin b12 831 pg / ml ) . however , we decided to stop lenalidomide treatment and observed him for 14 months ; at this time , 5q was detected in 8/10 metaphases and in 60% of the interphase nuclei ( hb 12.1 g / dl , mcv 108 fl , vitamin b12 792 pg / ml , platelet count 182  10/l ) ; the patient was rechallenged with lenalidomide 10 mg for 21 days every 4 weeks ( fig . he responded to the reintroduction of lenalidomide , achieving complete cytogenetic remission after 3 cycles and continuing lenalidomide at a standard dose of 10 mg until the sixth course [ hb was 14 g / dl ( fig . 2 ) , mcv decreased to 99 fl and vitamin b12 decreased to 442 pg / ml , platelet count 122  10/l , wbc 3.03  10/l , and anc 2.2  10/l ] . cytogenetic and fish analysis were negative and no blasts were detected in bone marrow aspirate . we reduced the dose at 10 mg biweekly for 3 weeks every 28 days for 4 months ; then 5q was detected in 44% interphase nuclei ( fig . 1 ) , karyotype was not available , hb was 13.5 g / dl , mcv 100 fl and vitamin b12 280 pg / ml . then we changed the schedule with the dose of 5 mg for 21 days every 4 weeks for 6 courses , when 4/10 metaphases and 22% of interphase nuclei showed 5q ; hb was 13.9 g / dl , mcv 96 fl , vitamin b12 1,344 pg / ml , bone marrow blasts 3% , and a partial cytogenetic remission was obtained ( fig . we increased lenalidomide to 10 mg for 21 days every 4 weeks ( 6 cycles ) . in this period , we observed grade 3 neutropenia , and we started g - csf once a week for 5 months . after these 6 cycles , 1/10 metaphases and 4% of interphase nuclei showed 5q , no bone marrow blasts were observed , but the development of a new independent clone was detected by cytogenetic and fish analyses , containing loss of the y chromosome in 2/10 metaphases and in 28% of interphase nuclei ( fig . other parameters were : hb 14 g / dl , mcv 97 fl , vitamin b12 448 pg / ml , platelet count 105  10/l , wbc 3.3  10/l , and anc 1.2  10/l . we continued lenalidomide treatment for another 3 cycles at 10 mg dose , when 1/10 metaphases and 3% of interphase nuclei showed 5q and 3/10 metaphases and 31% of interphase nuclei were positive for loss of the y chromosome with hb 14.3 g / dl , mcv 98 fl , vitamin b12 411 pg / ml , platelet count 117  10/l , wbc 2.9  10/l , and anc 1.3  10/l . at this point , we decided to reduce lenalidomide at 10 mg every other day for 21 days of every 28-day cycle , and this schedule was administered for 6 cycles ; after that , 8/12 metaphases and 24% of interphase nuclei showed 5q , and 3/12 metaphases and 28% of interphase nuclei were positive for loss of the y chromosome with bone marrow blasts 3% , hb 12.2 g / dl , mcv 102 fl , vitamin b12 744 pg / ml , platelet count 132  10/l , wbc 2.5  10/l , and anc 1.08  10/l . then we increased lenalidomide dosage at 10 mg for 21 days of every 4-week cycle ; after 6 cycles , 7% of interphase nuclei showed 5q and 38% loss of y chromosome , bone marrow blasts 2% , hb was 13.6 g / dl , mcv 97 fl , vitamin b12 682 pg / ml , platelet count 91  10/l , wbc 2.42  10/l , and anc 1.17  10/l ; at present , this schedule is still administered . the patient has never taken a supplement of vitamin b12 , he continues thromboprophylaxis with aspirin ( 100 mg / day ) , no thrombotic events have so far been observed , he has a good quality of life , assessed with the functional assessment of cancer therapy - anemia ( fact - an ) questionnaire , and he continues to perform daily sport activity by jogging for 2 h a day since the first achievement of complete hematological and cytogenetic remission . consequences of the long - term effects of continuous immunomodulation with lenalidomide are unknown . furthermore , there is limited evidence that discontinuation of lenalidomide may lead to long - term transfusion freedom . our patient with ipss - defined low - risk mds with isolated 5q within 12 weeks of initiating lenalidomide 10 mg achieved ti and complete hematological and cytogenetic remission . he maintained ti from february 2008 until march 2014 ( 6 years ) also stopping lenalidomide for 13 months ( december 2010 to december 2011 ) ; in many cases reported in the literature , the median duration of ti is 2 years . we observed a correlation between cytogenetic response and normalization of mcv and vitamin b12 levels , with a decrease of the amount of abnormal interphase nuclei , showing 5q , detected by fish . long - term outcome data indicate that a cytogenetic response to lenalidomide therapy might offer a survival advantage , compared with cytogenetic nonresponders , and lenalidomide treatment does not increase aml progression risk , among lower - risk , transfusion - dependent mds patients , but instead confers a possible benefit in red blood cell transfusion - dependent patients with del(5q ) low- or intermediate-1-risk mds [ 9 , 11 ] . in our patient , after 5 cycles of standard treatment , we obtained complete hematological and cytogenetic remission ; we then tapered off the dose of lenalidomide , and the patient remained transfusion independent and in complete hematological and cytogenetic remission for further 9 months ( fig . 1 , fig . 2 ) . in november 2009 , the patient had a cytogenetic relapse remaining transfusion independent ; we , however , stopped lenalidomide and observed him . subsequently the patient was rechallenged with lenalidomide and he responded to the reintroduction of lenalidomide intervention as other cases described by giagounidis et al . , achieving complete cytogenetic remission after 3 cycles and continuing this dosage until the sixth course ( july 2011 ) . we continued to modulate the dose of lenalidomide on the basis of fish analysis ( table 1 ) ; in our patient , the reappearance of 5q was not equivalent to transfusion dependence and as in other patient series he remained transfusion - free , without being exposed for many months to any medication . mcv and vitamin b12 levels , in our case , have always correlated with the hematologic and cytogenetic response , normalizing when the patient achieved complete remission and rising again to more than the normal reference value when the patient relapsed , indicating in our patient a variation in the promotion of effective erythropoiesis . therefore , mcv and vitamin b12 values may be very simple parameters to monitor regularly . to our knowledge , this observation has never been stressed in previous publications and monitoring those easily available parameters could help , together with cytogenetic and hematological analyses , to follow the response and eventually to modulate the lenalidomide schedule , in a manner as to reduce drug toxicity ; specially if the patients maintain a good hematological response with ti , at least in low - risk mds patients analyzed the relationship between the development of treatment - induced cytopenias and the response to therapy in mds . they specifically found that among lower - risk mds patients with del(5q ) whose platelet count decreased by 50% , packed red blood cell ti was likely to be achieved , as compared with patients not experiencing the same magnitude of thrombocytopenia ; however , they did not analyze mcv and vitamin b12 as parameters that predict the response . also in our case we registered a platelet count of less than 150  10/l ( range 91149  10/l ) , except after 14 months of stopping treatment , when the platelet count was 182  10/l and 5q was detected in 60% of interphase nuclei ; however , we still observed ti but hb decreased to 12.1 g / dl . a platelet count decline was again evident after the restart of lenalidomide treatment ; a platelet drop was also present when we used the schedule 5 mg for 21 days or every other day or biweekly . with the dose of 5 mg biweekly that , compared to the schedule of 5 mg every other day , was never published , we still had ti and a progressive normalization of the platelet count but eventually an increase in 5q and interphase nuclei . six and a half years after the diagnosis and 5 years after the onset of lenalidomide treatment , we registered in our patient the development of a new independent clone with the loss of the y chromosome , detected in both conventional cytogenetics and fish . the deletion of the y chromosome in men was not considered abnormal in a previous study ; the clinical association between the loss of the y chromosome and aml / mds is still debated because both phenomena are related to aging . it has been demonstrated that normal males start to lose the y chromosome in bone marrow cells at the age of 60 years , and in a series of 142 patients with loss of y chromosome the cases with karyotype , demonstrating less than 100% loss of the y chromosome , were not statistically associated with aml / mds . our patient was 60 years old at diagnosis and developed loss of y chromosome in about 30% of cells at the age of 65 , 5 years after the start of lenalidomide treatment , with periods of discontinuation of treatment and dose tapering . clearly , the loss of y chromosome is still a gray zone and we will thus continue to monitor our patient . treatment with lenalidomide improved health - related quality of life ( fact - an ) ; improvements were apparent at week 12 and were significantly demonstrated through 6 years , with absolute change from baseline fact - an scores exceeding 7 points . neutropenia grade 3 was the most common treatment - associated adverse event , no venous thromboembolism was registered , but aspirin as thromboprophylaxis was administered . current recommendations state that treatment with lenalidomide in del(5q ) mds should be continued until disease progression . the question whether interruption of lenalidomide treatment is beneficial in patients in remission has never been formally addressed . this concept is appealing for several reasons : first , it would reduce costs and side effects ; second , the progression to aml in 5q disease is not entirely understood . reducing lenalidomide exposure would prevent a notional selective pressure of the compound on 5q stem cells , facilitating disease progression . it has been speculated that continuous administration of lenalidomide may lead to selective pressure on stem cells that induces genomic instability , resulting in acute leukemia transformation . our patient , as other cases in the literature , remained in long - term complete cytogenetic remission without lenalidomide treatment , before showing reappearance of 5q . the reappearance of 5q is not equivalent to transfusion dependence and many patients remain transfusion free for years without being exposed to lenalidomide ; in our case , the restart of lenalidomide treatment did not result in a very profound cytogenetic response compared to using lenalidomide as a first - line treatment . in our case , lenalidomide interruption was safe and feasible as also reported in other mds patients with 5q of low and intermediate-1 risk according to the ipss . mcv and vitamin b12 levels could help together with platelet count decline to predict the response .