By Dr. Karsten Fostvedt
Melanoma is a tumor that arises cells that produce a pigment called melanin. Melanomas in the mouth of dogs are often extremely malignant and require early, aggressive surgery for a successful outcome. Oral melanoma is one of the most common malignant cancers in dogs. No direct cause of oral melanoma has been identified in dogs. Most dogs are older, and many breeds are affected.
The main finding is a mass inside the mouth arising from the gums or the roof of the mouth. Clinical signs include bad breath, bleeding from the mouth, loss of appetite, face rubbing and trouble chewing or swallowing. In many cases, the tumor is found during a routine physical exam. Metastasis, or spread of oral melanomas, is common to lymph nodes, the lungs and nearby bone, which can lead to tooth loss.
Definite diagnosis is only made by submitting tissue samples of the tumor to a veterinary laboratory to be read by a pathologist. This biopsy usually requires general anesthesia. These tumors can invade deeper tissues, so the primary biopsy may not be curative; and often second and even third surgeries are necessary to adequately remove the melanoma completely. Laboratory tests, such as chest X-rays, lymph node biopsies, skull X-rays and abdominal ultrasounds are also necessary to search for metastasis of this highly malignant tumor.
Your veterinarian may recommend referring your dog to a cancer specialist for staging and treatment planning. The main treatment is surgical removal of the tumor, with wide margins of normal issue also being removed. This can often be difficult in the mouth. Obtaining wide margins may require removal of teeth or portions of the upper and lower jawbones. Following surgical removal, radiation therapy is often recommended to kill any cancer cells remaining at the surgical site.
A recently introduced therapy for oral melanoma involves the administration of a vaccine that stimulates the dog’s own immune system to kill melanoma cells. This vaccine is started after surgical removal of the primary tumor. The vaccine is most effective when the original tumor was small, a successful surgery was performed, and there is no evidence of metastasis to the lymph nodes or lungs. Oral melanoma, without extensive surgery, radiation and this new vaccine has a poor prognosis in dogs. Even with the above, many dogs die within six to 12 months of the diagnosis.
Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.
