Mucoepidermoid carcinoma in an “Anal fistula” with associated adenocarcinoma in a villous adenoma of the descending colon

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Abstract
The concomitant findings associated with the villous adenoma add to the possibilities of modes of distant tumor manifestation. The case also emphasizes the validity of the controversy concerning tumor cell origin, since anal duct remnants have not yet been reported to occur in more proximal portions of the colon. The mucoepidermoid component of the villous adenoma must have arisen from this neoplastic site de novo. The existence of a spectrum of multipotential tumor cells within a particular neoplastic clone within the same organ system can be postulated to explain 2 separate sites of mucoepidermoid carcinoma. The evidence for this assumption is demonstrated by the histologic variety found within the malignant foci of the villous adenoma. That classic adenocarcinoma coexisted with distinct squamous and signet cell elements shows a multipotential cell situation, in which a single cell type might become metaplastic at any site and diverge in its differentiation to become squamous along 1 line, or signet cell along another. From the pathologic standpoint, this case is highlighted by 2 uncommon occurrences, a rare mucoepidermoid carcinoma within an anal fistula, and the fascinating divergent cellular patterns of the carcinoma associated with the villous adenoma.