Melanotic adenocarcinoma of the anorectum

A variety of tumors, besides those formed by melanocytes, may contain melanin pigment. Most of them have originated from the neural crest. Epithelial tumors with melanosomes are very unusual. We report the case of a 76-year-old woman with rectal adenocarcinoma that invaded the intestine and vagina extensively. At the anorectal site, melanin pigment was found in the cytoplasm of the malignant neoplastic epithelial cells, and melanosomes were ultrastructurally confirmed at various developmental stages. Melanocytes with cytoplasmic processes spreading between neoplastic cells were also present as the apparent source of the pigment contained in the neoplastic cells.