[A case of erythropoietin-producing renal cell carcinoma with a skin metastasis].

An 83-year-old man came to our hospital complaining of asymptomatic gross hematuria. We found a subcutaneous tumor in his chest and an abdominal mass in his left upper quadrant. Laboratory data showed red blood cell count of 737 x 10(4)/mm3 and hemoglobin level of 17.9 g/dl. The serum erythropoietin level measured by radioimmunoassay was considerably high. He underwent left nephrectomy and tumor resection in the chest wall. Serum erythropoietin level became normal following surgery and erythrocytosis disappeared. Histological findings revealed renal cell carcinoma, alveolar type, clear cell subtype, grade 2. The erythropoietin levels of the extracts of the cancer tissue and the normal kidney tissue were 2430 mU/g and 59.5 mU/g, respectively. Lung, liver and bone metastases appeared four months after the operation and serum erythropoietin level increased again.