Merkel cell carcinoma.

A 92-year-old man presented for evaluation with a 1-month history of a rapidly growing asymptomatic pink nodule on his forearm. Biopsy results of the lesion demonstrated pathology consistent with Merkel cell carcinoma (MCC). Immunohistochemical studies displayed positive cytoplasmic staining for cytokeratin AE1/AE3, positive dot-like perinuclear staining for cytokeratin-20, diffuse cytoplasmic staining for neuron specific enolase, and no significant staining for S-100. Subsequent positron emission tomography did not reveal evidence of metastatic disease. Wide excision of the lesion was performed along with a sentinel node biopsy of his left axilla. The sentinel nodes were negative for MCC. Adjuvant radiation treatment of the tumor site was provided because the pathologist noted MCC within 2 mm of the deep margin.