Ameloblastoma with basal cell carcinoma-like feature emerging as a nasal polyp

A case of a 63-year-old man with ameloblastoma with basal cell carcinoma (BCC)-like features clinically emerging as a nasal polyp is reported. The left nasal cavity was filled with a solid mass, which seemed to be a sinusitis-associated nasal polyp. The polyp was covered by parakeratotic squamous epithelium which was directly connected to the BCC-like tumor nest. The BCC-like features gradually changed to adamantinoid features. The polyp was connected with a huge mass filling the maxillary sinus and the molar area, which consisted of conventional ameloblastoma features. Although the tumor was finally diagnosed as an ameloblastoma of the maxilla, the biopsy specimen forced us to face the problem of differential diagnosis, ameloblastoma with BCC-like features or adamantinoid basal cell carcinoma (BCC). Immunohistochemical examination revealed that tumor cells of the ameloblastoma reacted with anticytokeratin antibody KL-1 but not with antiepithelial antibody Ber-EP4, and these reaction patterns were completely contrary to those of BCC. It is emphasized that immunohistochemical examination using anticytokeratin antibody KL-1 and antiepithelial antibody Ber-EP4 is a good tool for distinguishing ameloblastoma with BCC-like features from adamantinoid BCC.