Expression of neurofilament and neuron-specific enolase in small cell tumors of skin using immunohistochemistry.

Trabecular carcinoma of the skin (Merkel cell tumor), a neoplasm of putative neural origin, must be differentiated from other small cell tumors primary or metastatic to skin. In order to provide more objective diagnostic criteria, four were examined using monoclonal antibodies against neurofilament proteins (NF) and antiserum specific for neuron-specific enolase (NSE). Immunohistochemistry demonstrated immunoreactive NF in three and NSE in four cases. NF immunoreactivity was arranged in paranuclear balls, consistent with ultrastructural observations of aggregated intermediate filaments. A case of pulmonary oat cell carcinoma metastatic to the skin also contained immunoreactive NF and NSE. Although NF and NSE do not discriminate metastatic oat cell carcinoma from trabecular carcinoma of skin, they are useful antigens that provide objective criteria for recognizing tumors of neural histogenesis or neural differentiation. They should make it possible to exclude non-neural lesions from the differential diagnosis of small cell tumors of the skin.