Loss of Conventional Melanocytic Markers in Malignant Melanoma and Lymph Node Metastasis; an Uncommon but Dangerous Pitfall.

Although malignant melanomas exhibit a wide range of immunophenotypes, concurrent loss of all 3 conventional melanocytic markers (S-100, Melan-A, and HMB-45) is relatively rare. We report a case of primary malignant melanoma with lymph node metastasis, both exhibiting loss of immunoreactivity for conventional melanocytic markers, while aberrantly expressing epithelial antigenicity (pancytokeratin, CAM 5.2).