[Perirenal malignant perivascular epithelioid cell tumor originating from right retroperitoneum: a case report].

A 51-year-old woman was admitted to our hospital for detailed examinations and medical treatment against the right retroperitoneum tumor and liver lesions. Computed tomography showed a 20 cm diameter enhanced mass in the right perirenal space and multiple liver metastases. Pathological examination by needle biopsy revealed a perivascular epithelioid cell tumor (PEComa). With weekly administration of a mTOR inhibitor, Temsirolimus, the tumor was reduced by about 20% one month later. The maximal response was stable disease due to RECIST v 1. 1. However, shortly after the minimal response, the disease showed progression. She died about five months after the start of molecular targeted therapy. In regard to the origin of PEComa, our report is the fifth in Japan as a case of retroperitoneal origin to the best of our knowledge.