Immunohistochemical demonstration of simple epithelia-type keratin intermediate filament in a case of Merkel cell carcinoma.

A case of Merkel cell carcinoma that developed on the right cheek of a 77-year-old woman is reported. The diagnosis was ultrastructurally made by demonstrating dense-core granules in the cytoplasm of the tumor cells. Immunohistochemically, the tumor cells were shown to possess simple epithelia-type keratin intermediate filaments, but no neurofilaments. This finding was in accordance with that obtained on normal Merkel cells. No bioactive peptides examined could be detected in the tumor cells. Typing of intermediate filaments in tumor cells may be one of the important markers, along with the ultrastructural findings, in diagnosing Merkel cell carcinoma.