Cloacogenic carcinoma of the anorectum in homosexual men: an observation of four cases.

Cloacogenic carcinoma of the anorectum is an uncommon neoplasm which arises from the transitional zone (cloacogenic) epithelium. The transitional zone epithelium is derived from the embryonic cloacogenic membrane as is the epithelium of the vagina and uterine cervix in the female. Four cases of cloacogenic carcinoma in male homosexuals who have engaged in longstanding receptive and anal intercourse have been observed. This observation, along with the realization that the anorectal transitional zone shares a common embryologic origin with the uterine cervix, a site of cancer long known to be associated with factors related to sexual intercourse, leads to the serious question of the etiologic potential of receptive anal intercourse in the development of cloacogenic carcinoma.