A case series and immunophenotypic analysis of CK20-/CK7+ primary neuroendocrine carcinoma of the skin.

Background: The diagnosis of Merkel cell carcinoma (MCC) can be rather challenging; therefore, the immunohistochemical profile is important in confirming the microscopic diagnosis. Characteristic of the neuroendocrine and epithelial differentiation of MCC, antibodies to cytokeratin (CK) 20, CK7, epithelial membrane antigen, and neuron-specific enolase among others, are used in confirming the diagnosis. As reported in the literature, the majority of MCC express CK20 and are CK7 negative.