Peripherin, a neuronal intermediate protein, is stably expressed by neuroendocrine carcinomas of the skin, their xenograft on nude mice, and the corresponding primary cultures.

The histogenesis of neuroendocrine carcinomas of the skin is still controversial. To determine the degree of neural differentiation of these neoplasias, we studied the expression of intermediate filament proteins in tumoral tissues. Expressions of peripherin, the neurofilament protein NF-L, vimentin, and cytokeratin 8 were analyzed by immunohistochemical methods on 12 human primary tumors and 3 tumor xenografts on nude mice. Peripherin was detected in 10 primary tumors by immunofluorescence. The protein and the corresponding messenger RNA were identified by two-dimensional gel electrophoresis and Northern analysis in extracts of an immunofluorescence-negative tumor. Peripherin, NF-L, and cytokeratin 8 were detected in tumoral cells, whereas vimentin was found exclusively in the stroma. The histological and ultrastructural properties of the original cells of neuroendocrine carcinomas of the skin, as well as coexpression of peripherin, cytokeratin 8, and neurofilament polypeptides, were preserved in tumor xenografts and their primary cultures in vitro. These results bring new elements to the knowledge of the biology of neuroendocrine carcinomas of the skin and indicate that peripherin constitutes a marker for tumor identification.