A 9-year-old female Shih Tzu-Beagle mixed breed dog was referred to the hospital for treatment of difficulty in defecation and urination (Day 1). Palpation and abdominal ultrasonography revealed a mass in the right thyroid, left hepatic lobe and lower abdomen. Surgery was performed on Day 8, and thyroid carcinoma, hepatocellular carcinoma, and leiomyosarcoma were diagnosed histopathologically. After surgery, the general condition was good. Piroxicam (Palpasin; Towa Pharmaceutical Co., Ltd., Osaka, Japan) (0.3 mg/kg, eod) was administered orally from Day 16 to Day 89.

On Day 391, abdominal ultrasonography revealed a mass in the left hepatic lobe. The family did not want further treatment. The patient enjoyed an excellent quality of life for 1464 days until death resulting from liver tumor.

Canine oral melanoma is an aggressive neoplasm with recurrence and metastasis associated with poor prognosis. On the other hand, there are some recent papers describing well-differentiated oral melanocytic neoplasms. In the present communication, the authors report the prognosis of well-differentiated oral melanocytic neoplasms in five dogs.

Complete excision without recurrence was achieved in three of four dogs that underwent surgery. In one dog, incomplete excision was followed by growth of the residual tumor, leading to euthanasia. In the remaining four dogs, the cause of death was not related to the oral melanocytic neoplasm. Adjuvant chemotherapy was probably unnecessary, considering the absence of distant metastasis in all the five dogs. Survival duration from initial examination was 46.3, 15.6, 54.6, 23.3, and 52 months. Well-differentiated oral melanocytic neoplasms require treatment because the tumor gradually grows, causing feeding problems, bleeding, and respiratory failure. Surgical treatment alone is associated with a good prognosis, and curative treatment may be achieved by early complete resection.