Merkel cell carcinoma: a clinical, histopathologic, and immunohistochemical review.

Merkel cell carcinoma is a rare aggressive neoplasm, with about 400 cases diagnosed in the United States each year. Among the cutaneous-derived neoplasms, it is the most deadliest, with a higher mortality rate than melanoma. Although the classic clinical presentation as a rapidly growing papule in a sun-exposed site of an elderly patient is not specific, certain histopathologic and ancillary pathologic features allow for its discrimination in most cases. Herein, we review the etiology, pathogenesis, clinical, and pathologic attributes as well as the staging treatment and prognosis of this important public health menace.