Papillary clear cell adenocarcinoma of the groin arising from endometriosis

A 67-year-old woman presented with a rapidly enlarging right anterior thigh mars. Clinical impression uas of a primary sarcoma. but the histologic ana lysis of an incisional biopsy specimen showed adenocarcinoma with clear cel l differentiation. Initially thought to be a metastasis, the malignant tumo r appears to have arisen from extraabdominal endometriosis of the right gro in. This case shows clinical, radiographic, and histologic findings that ma g help the orthopaedic surgeon recognize an unusual complication of extrape lvic endometriosis.