Primary neuroendocrine (Merkel cell?) carcinoma of the skin. II. An immunocytochemical study of 21 cases.

Twenty-one examples of neuroendocrine carcinoma of the skin were examined by the unlabeled antibody enzyme method for several neural hormones and peptides, carcinoembryonic antigen, S-100 protein, neuron-specific enolase, and three intermediate filaments: neurofilament, glial fibrillary acidic protein, and cytokeratin. Vasoactive intestinal polypeptide from two sources reacted with the neoplastic cells of four (18%) and seven (32%) of the cases, and pancreatic polypeptide reacted with scattered cells of one case. Neuron-specific enolase reactivity occurred in 50% of the cases. Neurofilament (70, 150, 200 kilodaltons) was strongly positive in 40% of the tumors whereas neurofilament (200 kilodaltons) was negative. Two monoclonal anticytokeratin antibodies of 54 kilodaltons and 44-54 kilodaltons reacted in 77% and 64% of the cases, respectively, in a distribution similar to the neurofilament. Sections reacted with antisera against cytokeratins of higher molecular weight were negative. The demonstration of vasoactive intestinal polypeptide, pancreatic polypeptide, neurofilament, and neuron-specific enolase is evidence of the neuroendocrine nature of this neoplasm.