Primary squamous cell carcinoma of the colon arising in a villous adenoma.

The first case of pure squamous cell carcinoma arising in a villous adenoma of the cecum is reported, and the literature of squamous cell carcinoma of the colon is reviewed. The possible origin of this neoplasm in adenomas of the colon, similar to that of adenocarcinoma, is discussed, and the site distributions of adenocarcinoma and squamous cell carcinoma are compared. The distribution of primary colonic squamous cell carcinoma is found to be predominantly right-sided in comparison to adenocarcinoma (p less than 0.05). Although this result does not preclude adenomas as the origin of most squamous cell carcinomas, it suggests the influence of as yet unknown site-asymmetric factors that are different from those for adenocarcinoma.