Paraneoplastic Erythrocytosis of Colon Cancer, with Serum Erythropoietin within the Normal Reference Range

BACKGROUND Paraneoplastic erythrocytosis can be brought on by ectopic erythropoietin production usually in kidney, brain, and liver tumor with increase of serum erythropoietin level. We report here a paraneoplastic erythrocytosis of colon cancer with serum erythropoietin within the normal reference, which required an immunohistologic test for erythropoietin-antibody to be diagnosed. CASE REPORT Our case report was of a 75-year-old woman with erythrocytosis. Her hemoglobin and serum erythropoietin levels were 191 g/dL and 12.6 IU/L (reference range, 9.1-32.8), respectively. Colonoscopy revealed an advanced sigmoid colon tumor 20 mm in diameter. She underwent colectomy, and immunohistochemical examination showed the colon adenocarcinoma was focally positive for erythropoietin-antibody. One month after the surgery, her hemoglobin level decreased to 117 g/L. CONCLUSIONS Colon cancer can cause paraneoplastic erythrocytosis, and it is important to consider not simply the absolute serum erythropoietin level but also the serum erythropoietin level relative to simultaneously measured hemoglobin level. We should include paraneoplastic erythrocytosis as a differential diagnosis in cases of high hemoglobin level unexplained by other diseases.