Mucoepidermoid carcinoma of the anal canal: an immunohistochemical study.

We present a case of mucoepidermoid carcinoma of the anal canal, with special reference to immunohistochemical analysis of the tumor to clarify its histogenesis. A 36-year-old man underwent surgery for mucoepidermoid carcinoma of the anal canal. Immunohistochemical analysis of the resected specimen was performed. Serial sections were stained immunohistochemically by the labeled streptavidin-biotin peroxidase method for various antigens, including epithelial membrane antigen (EMA); carcinoembryonic antigen (CEA); different types of cytokeratins, including CK10 and CAM 5.2; and p53 oncoprotein. The solid component of the tumor cells was immunohistochemically positive for EMA, CEA, and CAM 5.2, but negative for CK10. These staining patterns were different from those of anal squamous epithelium. These results confirm that mucoepidermoid carcinoma of the anus may arise from the anal transitional zone, and that it is biologically different from squamous cell carcinoma of the anus.