An unusual
tumor of the skin was removed from the thigh of a 52-year-old white male. By light microscopy, the
tumor was composed of intermediate and small cells in sheets and clusters. Ultrastructural study of the
tumor cells showed numerous dense core granules and dendritic cell processes as well as intermediate filaments and cell junctions frequently within the same cells. Most of the
tumor cells were stained intensely by
antibodies to neurone-specific
enolase (NSE), a marker of cells of the central and peripheral nervous system. The
neuropeptides met-enkephalin and
vasoactive intestinal peptide (VIP) were also found in
tumor cells. Immunohistochemistry furthermore demonstrated
cytokeratin. Both the ultrastructural appearance and
keratin content of this
tumor set it apart from conventional Merkel cell (or trabecular)
carcinoma of the skin in a manner analogous to bipartite (i.e., epidermoid and
small cell) carcinoma of lung. The production of
neuropeptides simultaneously with the production of
keratin establishes this as a bipartite skin
tumor (i.e., ectodermal and neuroectodermal phenotype). We suggest that at least some primary
neuroendocrine tumors of the skin arise from multipotential ectodermal cells not of neural crest origin, as has been proposed for
small cell carcinoma of lung.