Basal Cell Carcinoma Arising within a Trichoepithelioma: An Immunohistochemical Study

Abstract

Background: Trichoepithelioma (TE) and basal cell carcinoma (BCC) of skin represent distinct tumor entities but they have a close histogenetic and phenotypic relationship.Objective: A unique case of a BCC arising within a TE is described with an emphasis on the analysis of different and for each tumor type typical immunophenotype.Material and Methods: A 71-year-old man presented with a subcutaneous solid tumor in the lumbar region. The resected tumor specimen was studied by immunohistochemistry.Results: Histology revealed a coexistence of classic TE and nodular BCC. Both tumors were strongly positive for BerEP4 and negative for EMA. Neoplastic epithelium of the BCC showed a diffuse staining for Bcl-2, while the TE expressed Bcl-2 almost exclusively in the peripheral cells of tumor islands. In the BCC, neoplastic nodules exhibited a focal staining for CD10, while the peritumorous stroma did not. In contrast, the TE showed a focal immunoreactivity for CD10 in the stromal cells around the neoplastic islands which were completely negative. The TE contained intratumorous CK20-labeled Merkel cells but they were not detected in the BCC. A stromal immunore-activity for CD34 was found in both tumors. Proliferative activity (Ki-67) was slightly higher in the BCC than in the TE.Conclusion: Although a concomitant presence of TE and BCC in the same skin lesion is a unique finding, it may be sometimes encountered in a biopsy practice. Pathologists should provide a careful histologic examination of the whole TE lesion with precise section sampling to unveil such possible association.