Neuroendocrine (Merkel-cell) carcinoma of the skin: immunocytochemical and cytomorphologic analysis on fine-needle aspirates.

Cytomorphologic and immunocytochemical characteristics of tumor cells from fine-needle aspirates of four neuroendocrine (Merkel-cell) carcinomas of the skin are described. All aspirates were cellular with dispersed small to medium sized tumor cells with scanty cytoplasm. Many mitoses were observed. Careful scrutiny revealed a tendency of the tumor cells to form microacinar and pseudorosette formations as well as small clusters of molding cells. Immunocytochemical analysis of cytospin preparations showed a peculiar dot-like cytokeratin positivity, while neuron-specific enolase staining was more diffuse. A weak S-100 positivity was observed. This staining pattern is highly suggestive of Merkel-cell tumor. It can thus be concluded that immunocytochemical analysis in conjunction with cytomorphology on fine-needle aspirates will allow the identification of neuroendocrine carcinoma of the skin and its differentiation from other small-cell neoplasias of the skin.