Unusual occurrence of a melanoma with intermixed epithelial component: a true melanocarcinoma?: case report and review of epithelial differentiation in melanoma by light microscopy and immunohistochemistry.

We report a case of a 27-year-old woman with a nonpigmented lesion on the right scalp. Histological examination showed a malignant nodular neoplasm with 2 distinct but intimately admixed components: a malignant melanoma with a spindle component and an unusual glandular component. Immunohistochemical studies demonstrated epithelial differentiation on the basis of cytokeratin (CAM5.2 and AE1/AE3) expression in the glandular component and melanocytic differentiation (HMB-45, PNL2, MITF, and S-100) of the spindle cell component. A single melanocytic marker (MITF) was expressed in both components, raising the possibility of dual differentiation in a single tumor, rather than the alternative considerations of a collision tumor or a reactive pseudoepitheliomatous hyperplasia with eccrine duct lumen formation within a melanoma. This unusual tumor with both melanocytic and epithelial components may represent a true melanocarcinoma, which becomes a plausible consideration, in view of melanoma plasticity and recent experimental evidence and speculation about the role of stem cells in melanoma.