Current Concepts on Cloacogenic Transitional Cell Anorectal Cancers

The uncommon, cloacogenic, transitional cell, anal cancers are newly recognized clinicopathologic variants of the better-known, keratinizing, squamous cell malignancies. These unusual nonkeratinizing lesions arise at the narrow membranous anorectal junctional zone, from sometimes persisting cloacogenic transitional cell remnants. Transitional cell cancers occasionally have histological patterns mimicking nonmetastasizing basal cell epitheliomas and have been labeled "basaloid" cancer by some investigators. Three distinctive subdivisions are included within the new category of anal cancers. Treatment is radical abdominoperineal resection. Well-differentiated transitional cell cancers have a reasonably good prognosis. Local block excision has been a very effective treatment for "in situ" and small noninfiltrating tumors. Moderately differentiated transitional cell lesions or mixed patterns containing squamoid elements are more aggressive tumors. The rare, undifferentiated, anaplastic, "small cell basaloid" cancers are invariably lethal, despite radical surgical treatment.