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 (B CC)-like features clinically emerging as a nasal polyp is reported. The lef t nasal cavity was filled with a solid mass, which seemed to be a sinusitis -associated nasal polyp. The polyp was covered by parakeratotic squamous ep ithelium which was directly connected to the BCC-like tumor nest. The BCC-l ike features gradually changed to adamantinoid features, The polyp was conn ected with a huge mass filling the maxillary sinus and the molar area, whic h consisted of conventional ameloblastoma features. Although the tumor was finally diagnosed as an ameloblastoma of the maxilla, the biopsy specimen f orced us to face the problem of differential diagnosis, ameloblastoma with BCC-Iike features or adamantinoid basal cell carcinoma (BCC). Immunohistoch emical examination revealed that tumor cells of the ameloblastoma reacted w ith 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 disti nguishing ameloblastoma with BCC-like features from adamantinoid BCC.