Granular basal cell tumors in the skin of three dogs: a distinct histopathologic entity.

Granular cell variants of cutaneous basal cell tumors from three dogs are described. These tumors resemble a granular cell variant of basal cell tumor (carcinoma) in man. The tumors are characterized by classical basal cells as well as granular cells with numerous cytoplasmic granules. These granules are cytoplasmic vacuoles 0.3 micrometer to 1.5 micrometer that seem to be secondary lysosomes; they usually contain many small (42 nm), membrane-bound vesicles. No natural, non-neoplastic counterpart of these granular cells is known to exist in the skin, and the significance of the production and accumulation of the small vesicles is not known. The cytoplasmic granules, and their contents, resemble the granules of granular cell "myoblastoma" although granular basal cells are of epithelial origin.