Oral Melanoma

Oral malignant melanomas comprise about 30-40% of all malignant tumors in dogs, and occur most frequently in older, smaller, male dogs. Oral cancers are most common in cocker spaniels, Labrador retrievers, and other larger breeds. Common signs of oral melanoma are drooling (sometimes with bloody saliva), decreased eating, and halitosis (bad breath). Other signs may include coughing, difficulties in swallowing, and weight loss. Boxers also suffer from a vigorous development of tumor masses on their gums and around the teeth, which can pose physical problems during eating.

Oral melanoma tends to occur on the buccal mucosa, but may also be found on the gingival, palatine, or alveolar mucosa. Bony involvement of the cancer is variable when oral melanoma occurs on the latter three sites. The melanomas may be either pigmented or unpigmented, but the absence of melanin does not affect the prognosis. Tumors smaller than 1 centimeter in size offer the best prognosis, because larger melanomas often metastasize in the early stages to the regional lymph nodes, lungs, and other organs. If the dog is already has metastases at the time of diagnosis, the disease is advanced, and the prognosis is poor.

Oral melanomas are diagnosed by physical examination, with a biopsy, and radiographic studies.

Treatment of Melanoma

Surgical excision and radiation are used to treat oral melanoma in dogs. Because complete excision of the cancer is often difficult and tumor recurrence is common, the prognosis even after surgical excision is poor. The median survival time for dogs with oral melanoma is 8 months after diagnosis. Adjuvant therapies such as chemotherapy, immunotherapy, and experimental gene therapy are often applied because of the cancer's high rate of metastasis.

Antiangiogenic therapy is another potential novel treatment for canine melanoma. Early melanomas grow above the basement membrane of the skin and mucous membrane and are isolated from a blood supply. Invasive melanomas have induced angiogenesis, and they begin invading deeply into the local tissues. The tumor vascular channels permit melanoma cells to metastasize to other regions of the body. In human patients, a number of angiogenesis inhibitors have been studied in clinical trials, including Didemnin B, interleukin-12, and interferon alfa.