Immunosuppressive therapy is related to the increasing frequency of malignancies after transplantation. A small percentage (4.6%) of malignancies seen in kidney transplant patients are renal cell carcinomas (RCC) which occur almost exclusively in native kidneys. The prognosis of RCC largely depends on the presence of metastasis. Metastatic disease is very rare in small renal masses. In this case report, we aimed to present our case of approximately 4 cm-mass of metastatic RCC in our kidney transplant patient. During the examination due to exhaustion and weight loss, multiple suspicious metastatic lesions were observed in non-contrast computed tomography. In the patient who had multiple bone metastases on the whole-body bone scintigraphy, prostate cancer metastasis was considered in the first plan due to a history of prostate cancer before transplantation. This diagnosis could not be supported with prostate-specific membrane antigen-positron emission tomography/computed tomography (PSMA-PET/CT) scan. Whole body 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) was performed. A hypermetabolic mass lesion in the left kidney, multiple hypermetabolic lesions in the liver, in the left aortorenal junction, and in the skeletal system were observed. A biopsy was performed from the metastatic mass in the right lobe of the liver and the result was reported as renal cell carcinoma metastasis. Immunohistochemistry evaluation demonstrated positive staining for PAX-8, CK19, CD10 and negative staining for CK7, CK20, GATA-3, NAPSIN A, TTF-1, PSAP, glutamine synthetase and arginase. With all these findings, it was thought that the primary of metastases was the 4-cm mass in the left native kidney.

Keywords : kidney transplant, distant metastasis, small renal mass, renal cell carcinoma, immunosuppression