An unusual rectosigmoid mass: endometrioid adenocarcinoma arising in colonic endometriosis: case report and literature review.

Malignant transformation is an infrequent complication of endometriosis. The ovary is the primary site in 79 per cent of cases, and extragonadal sites are identified in 21 per cent. Primary involvement of these types of tumors with the colon and/or rectum is a rare clinical entity. Endometrioid carcinoma is a common histologic type that remains a diagnostic challenge-the main differential diagnosis includes colorectal carcinomas. We report a case of malignant transformation arising in colonic endometriosis. The patient had a total abdominal hysterectomy and bilateral salpingo-oophorectomy 10 years before she presented with hematochezia. The patient was ultimately treated by surgical resection. Immunohistochemical staining in addition to the usual histopathology was critical for accurate diagnosis of this endometriosis-associated intestinal tumor.