Basal cell carcinomas are populated by melanocytes and Langerhan's cells

Several reports have documented the coexistence of basal cell carcinoma (BC C) with other lesions, including melanoma. This study was performed to dete rmine whether nests of BCC contain benign melanocytes and Langerhan's cells . Ten cases of BCC were investigated to determine whether benign melanocyte s and Langerhan's cells populate tumor nests. The BCCs were stained with an tibodies to cytokeratin AE1/AE3, S-100, HMB-45, Melan-A, and CD1a proteins. We report that all 10 BCCs were populated by dendritic melanocytes distrib uted at the periphery (5/10 cases) or evenly throughout tumor nests (5/10 c ases). Clusters of melanocytes were not identified in any of the BCCs. A to tal of 9 of 10 tumors showed staining of dendritic Langerhans cells with CD 1a. A total of 8 of 10 tumors stained with cytokeratin AE1/AE3; in 6 of the 8 tumors, the staining was focal. We compared these findings with a single example of a BCC and melanoma in situ (MIS) collision tumor in which the c ytokeratin AE1/AE3-positive epithelial nests of BCC were populated by a hig h density of malignant melanocytes that stained with S-100 and HMB-45. Mela nocytes were disposed singly and in clusters of two or more cells within BC C tumor nests. We conclude from this study that BCCs are regularly populate d by benign melanocytes and Langerhan's cells. Furthermore, when BCC is inf iltrated with malignant melanocytes of MIS, the melanocyte density is highe r and clusters of melanocytes can be observed. The significance of these tw o findings is unclear, as additional cases of BCC MIS collision tumor need to be studied.