Merkel cell carcinoma: a report of three cases with neurone-specific enolase activity.

Three cases are described of a primary cutaneous neoplasm occurring in elderly patients, histological and immunohistochemical features of which support an origin from Merkel cells. Microscopically sheets of uniform small cells filled the dermis, often with a prominent trabecular pattern. Ultrastructurally the cells showed neurosecretory granules, tangles of microfilaments, scattered mitochondria and occasional intranuclear rodlets. Immunohistochemical staining for neurone-specific enolase was positive and for prekeratin was negative in each case. The definitive diagnosis of Merkel cell tumour can be made with a combination of electron microscopy and immunohistochemistry.