The rectum is the site of extensive replacement by squamous epithelium showing varying degrees of dysplasia as well as intraepithelial and focal superficial invasion by squamous cell carcinoma. The tumor has a basaloid growth pattern consistent with cloacogenic carcinoma derived from the transitional mucosa at the junction between the rectum and anus. The colonic mucosa shows mainly quiescent changes consistent with longstanding inflammatory bowel disease however focal ulceration and acute inflammation is present. Of note is the presence in the rectum for fissure formation which favors long standing Crohn's disease. There may have been underlying Crohn's disease which produced anorectal fissures which overtime led to healing with squamous metaplasia. Subsequently this transitional epithelium underwent malignant change to a cloacogenic form of squamous cell carcinoma.
Contributed by Jeff Nine, M.D. and Lina Perry, M.D.