Erythropoietin-producing renal cell carcinoma arising from acquired cystic disease of the kidney.

A 49-year-old woman had been on hemodialysis for 18 years. She presented with left back pain and macrohematuria. Radiologic studies demonstrated a left renal tumor with acquired cystic disease of the kidney. Her serum erythropoietin (EPO) level was 78.4 U/L despite no history of EPO supplementation. Left radical nephrectomy was performed. Pathologic examination revealed EPO-producing renal cell carcinoma. After surgery, the patient's serum EPO level decreased markedly to 15.1 U/L. The measurement of serum EPO levels may be useful for detecting and monitoring a recurrence of renal cell carcinoma with acquired cystic disease of the kidney in patients on long-term hemodialysis.