Renal cell carcinoma with erythrocytosis and elevated erythropoietic stimulatory activity.

A case study is presented of a 55-year-old man who had clear cell renal carcinoma with pulmonary metastases and erythrocytosis. The increase in red blood cell mass was associated with an elevation in erythropoietic stimulatory activity in serum, pleural fluid, and tumor-cyst fluid as determined by the exhypoxic polycythemic mouse assay. It is postulated that the increased erythropoietic stimulatory activity represents autonomous tumor secretion of erythropoietin or an erythropoietin-like material. Electron microscopic studies confirmed the proximal tubular origin of this tumor.