Squamous cell (epidermoid) carcinomas make up the majority of all primary cancers of the anus. The important subset of cloacogenic (basaloid transitional cell) tumors constitutes the remainder. These two histologic variants are associated with human papillomavirus infection.[1] Adenocarcinomas from anal glands or fistulae formation and melanomas are rare. Treatment of anal melanoma is not included in this summary.

References:

1. Palefsky JM, Holly EA, Gonzales J, et al.: Detection of human papillomavirus DNA in anal intraepithelial neoplasia and Anal Cancer. Cancer Res 51 (3): 1014-9, 1991.