Malignant degeneration of rectal endometriosis.

Background: Endometriosis is a relatively common disease among women with child-bearing potential, and rare before puberty or following menopause. It consists of the presence of hormone-responsive endometrium outside the endometrial cavity.

Case Report: We report the case of a patient with a rectal lesion, initially approached as a primary rectal malignancy, where histopathology eventually revealed an adenocarcinoma arising from endometrial tissue in the colonic wall.