Clear cell renal cell carcinoma with small intestine invasion mimicking an intestinal tumor.

A 65-year-old man presented with asymptomatic retroperitoneal mass that had been detected on ultrasonography performed during a physical screening. He had no hematochezia, hematuria or any other symptoms. Tumor markers were normal, including alpha fetoprotein, carcinoembryonic antigen, neuron-specific enolase and cancer antigen 199. Abdominal CT demonstrated a retroperitoneal mass (white arrow) accompanied by significant thickening of the jejunal wall, involving the left kidney. After enhancement, the mass showed rapid enhancement at arterial phase and venous phase, showed washout at delayed phase. Multi-planar reformation revealed the mass involving the pancreatic tail and the left renal pelvis. Surgical resection was performed and pathological examination confirmed clear cell renal cell carcinoma involving pancreas and jejunum, with immunohistochemical results as follows: CK (partly +), Vimentin (partly +), Pax-8 (+), CD10 (+), P505s (partly +), CA-IX (+), TFE-3 (-), Syn (-), CgA (-), CD56 (+), S-100 (-), SOX-10 (-), HMB-45 (-), Desmin (-),CD117 (-), DOG-1 (-), Melan-A (-), SMA (-), CD34 (+), CD31 (+), CD68 (+), Ki67 (5%+). Discussion.