Neuroendocrine (Merkel cell) carcinoma with an intraepidermal component.

We present 11 cases of primary neuroendocrine (Merkel cell) carcinoma of the skin with an intraepidermal component that were identified in a larger review of Merkel cell carcinomas. Among these is a case with a follow-up of over 11 years in which the primary lesion appeared as bowenoid dysplasia, with subsequent recurrences as intraepidermal Merkel cell carcinoma with focal tubular differentiation, and then with dermal invasion and lymph node metastasis. In addition to immunohistochemical markers commonly used in the identification of Merkel cell carcinomas (neuron-specific enolase and cytokeratin), these tumors stained with Ber-EP4, an immunohistochemical marker used to identify carcinomas. We believe that these histopathologic and immunohistochemical features further confirm that Merkel cell carcinomas represent an epithelial tumor with the potential for neuroendocrine and adnexal differentiation.