Carcinoma of the anal canal: a study of 79 cases.

Seventy-nine cases of carcinoma of the anal canal treated initially by surgery and having a minimum follow-up of five years were reviewed. It was found that all of the tumors were basically squamous cell carcinomas. They were divided into five histologic categories: keratinizing squamous cell carcinoma (52 cases), nonkeratinizing squamous cell carcinoma (6 cases), basaloid squamous cell carcinoma (11 cases), squamous cell carcinoma with mucous microcysts (6 cases), and pseudoadenoid cystic squamous cell carcinoma (4 cases). There was considerable overlap among the categories. The neoplasms also were stratified according to depth of invasion: 4 into submucosa only, 30 into smooth muscle of the anal sphincter, and 45 into perianal tissue. There were no significant differences in survival among the histologic categories but marked differences relating to depth of invasion: none of the 4 patients with submucosal invasion died of tumor, whereas 8 of the 30 with smooth muscle invasion and 35 of the 45 with perianal tissue invasion did so. The histologic categories also did not differ significantly in regard to the rates of lymph node metastasis (either at the time of initial surgery or later) or local recurrence; however, the rate of distant metastasis was higher in pseudoadenoid cystic squamous cell carcinoma (three of four cases) than in the other categories (11 of 75 cases combined). Based on our pathologic and clinical findings, we believe that there is no entity "cloacogenic carcinoma," "transitional cell carcinoma," "basaloid carcinoma," or "mucoepidermoid carcinoma" in the anal canal separable from squamous cell carcinoma, and we therefore suggest that these terms be dropped (or restricted to appropriate tumors in other locations). Pseudoadenoid cystic squamous cell carcinoma was the most distinctive of our histologic categories and is deserving of further study.