Perivascular epithelioid cell tumor (PEComa) of the pancreas: Immunoelectron microscopy and review of the literature

A perivascular epithelioid tumor (PEComa) is a rare tumor probably arising from the perivascular epithelioid cells. Only three cases of pancreatic PEComa have been reported in the English‐language literature. The present report describes an extremely rare case of pancreatic PEComa. A 47‐year‐old Japanese woman complained of lower abdominal pain and a well‐demarcated solid tumor was found in the pancreatic head. There was no history of tuberous sclerosis complexes. Pylorus‐preserving pancreaticoduodenectomy was thus performed. There was a well‐demarcated, solid tumor measuring 17 mm in the pancreatic head. The tumor was composed of a diffuse proliferation of epithelioid tumor cells with many blood vessels but no adipose tissue. The tumor cells expressed HMB45 and α‐smooth muscle actin. Ultrastructurally, the tumor cells possessed many membrane‐bound granules that were positive for HMB45 on immunoelectron microscopy. The results of immunoelectron microscopy show that some PEComas possess not only typical melanosomes or premelanosomes but also aberrant melanosomes.