Basal cell tumor in a Japanese macaque (Macaca fuscata).

A rare case of basal cell tumor of the skin in a wild-caught female Japanese macaque (Macaca fuscata) was studied. Tumor growth, which was composed of cells resembling basal cells, was observed in the dermis and subcutis and showed a mixture of ribbon, solid, glandular, and cystic patterns. The tumor was separated from surrounding normal tissue by a compressed zone of fibrous connective tissue. The nuclei were round and hyperchromatic and possessed a single centrally located nucleolus. Mitotic figures were common. Immunohistochemically, a positive reaction for epithelial membrane antigen, keratin, and cytokeratin AE3 was evident. Electron microscopic examination revealed a small number of tonofilaments in the cytoplasm.