Ultrastructural study of a mucinous carcinoid of the skin.

A tumor of 60 years' duration overlying the sternum of an 87-year-old woman is described. Histologically, the tumor was composed of lobules and cords of epithelial cells with finely granular, eosinophilic cytoplasm. The epithelial nests were floating in large pools of mucinous stroma, separated by thin fibrovascular septa. Cytoplasmic argyrophilia was seen by Grimelius silver stain. Positive reactions of the tumor cells were also found for chromogranin and neuron-specific enolase. Ultrastructural study revealed that the cytoplasm of the tumor cells contained two types of granules: neurosecretory and mucinous. From these findings, the present tumor is considered to be a carcinoid tumor with amphicrine cells, and the term "mucinous carcinoid" of the skin seems to be appropriate for the diagnosis of the present case.