the institutional review board approved this case report prior to any review of medical records .
an 80-year - old man was transferred to our institute because of an incidentally detected renal tumor .
the patient underwent a right partial nephrectomy due to a previously diagnosed rcc eight years prior .
recent routine follow - up ct images , which covered the lung and abdomen , revealed a right renal mass , a right adrenal mass , and three pulmonary nodules ; all of which were not seen on prior ct images ( figs .
1a - c ) . the right renal tumor and adrenal tumor had maximum diameters measuring 2.0 cm and 1.8 cm , respectively .
in addition , the pulmonary nodules , with maximum diameters ranging from 8 to 10 mm , were seen in the right upper lobe , left upper lobe , and left lower lobe .
the treatment modality decided upon was an rf ablation for the cytoreductive removal of the right renal tumor .
however , the histological results were not confirmed before the ablation as these lesions were clinically considered to be recurrent or as metastatic lesions from the previously removed rcc . an internally - cooled rf system ( radionics , burlington , ma )
was used for the ablation of the right renal tumor , along with an electrode ( cool - tip , valleylab , boulder , co ) that was kept below 20 by means of chilled water supplied by a peristaltic pump .
we selected an rf electrode with a 2 cm active tip , which corresponded to the size of the right renal tumor .
the electrode was appropriately targeted in the center of the renal tumor under ultrasound ( us ) guidance and performed two cycles of rf ablation . for the first ablation cycle ,
for the second rf cycle , reduced electrical power ( 80 w ) was delivered for 3 minutes due to severe pain . for pain relief , a total of 50 mg of penthidine hci ( hana pharmacy corporation , hwasung , korea )
was intravenously infused during the rf ablation . a post - ablation ct performed 10 months after the ablation showed a lack of tumor enhancement within the right renal tumor ( fig .
the size of the recurrent renal tumor decreased to a maximum diameter of 1.4 cm .
all of the metastatic pulmonary nodules became too small to be measured on ct images ( fig .
in addition , the right adrenal tumor decreased in size to a maximum diameter of 1.4 cm ( fig .
chemotherapy and immunotherapy was not performed due to the poor general condition and old age of the patient .
spontaneous tumor regression has been reported to occur for some types of malignant tumors , although the incidence is rare .
this phenomenon may be defined when the tumors partially decrease or totally disappear without any treatment .
an rcc can be a spontaneously regressing tumor and is in fact known to develop in less than 1% of rcc cases ( 1 - 5 ) .
spontaneous regression of metastatic lesions from an rcc have occurred frequently following a nephrectomy , radiotherapy , or embolization ( 1 - 4 , 6 ) . as with our case , metastatic pulmonary lesions were reported to spontaneously regress following an rf ablation of a tumor ( 7 ) .
these cytoreductive treatments seemed to play a major role in the spontaneous regression ; however , the role of nephrectomy accounted for only less than 50% of all reported cases with spontaneous regression ( 4 ) .
immunological responses to an rcc are also quite controversial , but the use of interferon to strengthen the hosts immunity , which may ultimately improve the survival of patients with advanced stage rcc should be performed ( 8) . in general , here has been a consensus that an rf ablation can be used in treating patients with a localized rcc , which is difficult to remove surgically .
recently , this treatment modality has been considered as a good alternative treatment option because of its minimally invasive nature and excellent clinical outcome .
for this reason , an rf ablation might be as beneficial as a nephrectomy at inducing the spontaneous regression of rcc , although their mechanisms are unknown .
both the rf ablation and a nephrectomy may be involved in stimulating the host 's immune system as if these treatments naturally kill the cells of rcc as with the use of immnunotherapy using interferon .
a literature search revealed that our case was found to be the second case report on the spontaneous regression of pulmonary metastases following an rf ablation of the recurrent rcc ( 7 ) .
however , we could not find any cases with spontaneous regression of adrenal metastasis from the rcc following ablation .
the rf ablation might be recommended as a good alternative treatment when a cytoreductive nephrectomy is required in patients with metastatic lesions , but are in poor general physical condition . in conclusion ,
spontaneous regression of metastatic lesions from an rcc is extremely rare , but can result following the rf ablation of the tumor .
 the spontaneous regression of metastatic lesions from renal cell carcinoma ( rcc ) is extremely rare , but may be encountered following cytoreductive treatments . 
 we report a case of a recurrent rcc with multiple metastatic lesions which spontaneously regressed after undergoing radiofrequency ablation of the renal tumor . 