Gingival osteogenic melanoma in two dogs

Osteogenic melanoma is a rare variant of metaplastic malignant melanoma in human medicine and appears to be a similarly rare variant in dogs. Two dogs with oral malignant melanoma with neoplastic bone formation are reported in this study. Both tumors were characterized by malignant melanocytes that transitioned into neoplastic bone at the deep margins of the neoplasm. Immunohistochemical analysis revealed S100- and Melan-A-positive neoplastic cells adjacent to, and occasionally embedded within, an osteoid and chondroblastic matrix. Scattered clusters of neoplastic cells were also positive for osteocalcin. The findings indicate that in dogs, as in humans, neoplastic melanocytes have metaplastic potential and can be osteogenic.