Biphasic malignant melanoma adenocarcinoma in the digit of a dog.

A 7-y-old Black Russian Terrier dog was evaluated for chronic lameness of the right forelimb and concurrent weight loss. Clinical examination revealed a pigmented mass arising from digit 4 of the right forelimb; the digit was amputated and submitted for histologic evaluation. Histologically, the neoplasm was composed of ill-defined streams, sheets, and clusters of melanocytes admixed with a distinct population of malignant epithelial cells forming glands and nests. The diagnosis was a biphasic malignant melanoma adenocarcinoma, a rarely reported neoplasm in human medicine that has not been described in veterinary medicine, to our knowledge.