Merkel cell carcinoma with seborrheic keratosis: A unique association.

Merkel cell carcinoma (MCC) is a rare, clinically aggressive neuroendocrine carcinoma of the skin; MCC is 40 times less common as compared to melanoma. The most frequently reported sites have been the head and neck, extremities, and trunk. Potential mimics include malignant melanoma, lymphoma, or metastatic small cell (neuroendocrine) carcinomas. Histopathology of MCC resembles small cell carcinoma both morphologically and on IHC. The possible cell of origin was proposed as the Merkel cell, which functions as a mechanoreceptor. It has a high chance of local recurrence, regional and distant spread. In recent times, Merkel cell polyomavirus has been implicated as the causative agent for this tumor. The same agent has a reported etiologic association with other skin lesions, including seborrheic keratosis.