Merkel cell carcinoma: squamous and atypical fibroxanthoma-like differentiation in successive local tumor recurrences.

Merkel cell carcinoma (MCC) is a rare, frequently lethal, primary neuroendocrine carcinoma of the skin. Histopathologically, it appears as a dermal nodule of small, undifferentiated malignant cells. Historically, MCC was considered to be an eccrine carcinoma.