Disseminated oral melanoma with brain and gastrointestinal tract involvements in a Cocker Spaniel: a case report.

A nine-year-old, male Cocker Spaniel with a history of surgical excision of oral melanoma located at the gingiva of the left maxilla was evaluated progressively over the course of 1 month post-surgery. The dog had shown signs of respiratory distress. Radiographic examination revealed diffusely pulmonary metastases. The respiratory distress progressively worsened and the dog died following excision of the oral mass. On necropsy, disseminated metastases to various organs including the lungs, heart, mediastinum, liver, kidneys, spleen, tonsil, lymph nodes, adrenal glands, thoracic wall, jejunum, pancreas, and brain were observed. Microscopically, the neoplastic cells were characterized by spindle to polyhedral phenotypes, having centrally located vesicular nuclei with prominent nucleoli, and melanin pigment accumulations in the cytoplasm. Neoplastic cells were seen within organ parenchyma as well as being found as emboli in blood and lymph vessels of those organs. The neoplastic cells demonstrated strongly cytoplasmic immunoreactivity to Melan A. Hematogenous dissemination is considered as an important route for distant metastases of oral melanoma. In this report, we describe the rare disseminated metastasis of an oral melanoma to the brain and gastrointestinal tracts, which are considered to be important sites of melanoma metastases in humans.