Melanoma is cancer of melanin-producing cells (known as melanocytes). Melanin is a dark pigment that normally provides color to the skin, hair, and eyes.
Melanomas can occur in the:
Mouth (oral melanoma)
Melanoma usually appears as a small growth or tumor on or under the skin, inside the mouth, or on the iris (the colored portion of the eye). Sometimes the tumor will be very dark in color, which tends to alert veterinarians to be concerned, but this is not always the case. It may also appear swollen, painful, and ulcerated, meaning that it looks moist or oozes.
Most types of melanoma are benign, meaning they do not cause damage, they do not invade or change the surrounding tissues, and they do not metastasize or spread to other parts of the body.
Oral melanoma tends to be malignant and very aggressive. This means that it can grow quickly, cause a lot of tissue damage, and spread quickly throughout the body. Oral melanoma is the most common oral tumor found in dogs.
Cause of Melanoma
Veterinarians don’t know why melanoma occurs. Unlike in people, it is not associated with sun or ultraviolet light exposure.
Staging and Survival
Your veterinarian will measure the tumor and examine nearby lymph nodes. The tumor, and in some cases, the lymph nodes will need to be biopsied, meaning a portion of them will need to be removed and examined by a veterinary pathologist to diagnose melanoma and determine what stage of melanoma is present. Bloodwork and X-rays may also be necessary to determine if the melanoma has spread.
Stage I: Tumor is less than two centimeters in diameter and disease has not spread to the lymph nodes or other organs
Stage II: Tumor is 2-4 centimeters in diameter and has not spread to the lymph nodes or other organs
Stage III: Tumor is greater than four centimeters in diameter and the cancer has spread to the lymph nodes but not to any other organs
Stage IV: The tumor, regardless of its size, has spread to organs other than the nearby lymph nodes
Oral melanoma is a deadly cancer. Studies have shown that most dogs with stage II or stage III oral melanoma live less than 5-6 months, even with surgery to remove the tumor.
Common treatment options for oral melanoma in dogs include surgery to remove the tumor and radiation therapy to treat any cells not removed by surgery or to treat melanoma cells that have spread. Chemotherapy can be used in some forms of melanoma, but it does not seem to work well for oral melanoma.
Melanoma Vaccine in Dogs
Oncept® is a vaccine licensed and labelled for use in dogs with stage II or stage III oral melanoma. The vaccine is typically used after other treatments have been done to remove as much of the tumor as possible.
How the Melanoma Vaccine Works
Oncept® is a DNA-based vaccine, meaning it triggers the dog’s immune system to specifically fight a protein associated only with melanoma tumor cells. It works on stage II and stage III oral melanoma, in addition to surgery and radiation, to increase the dog’s survival time.
The vaccine is given transdermally (beneath the skin) once every two weeks for four doses (i.e. every two weeks for two months) followed by a booster melanoma vaccine every six months.
Many studies have been performed and the melanoma vaccine in dogs has been shown to be very safe. The vaccine can be given to any dog, regardless of additional illnesses or poor health.
Side effects may include:
Decreased activity level
Where to Get the Vaccine
Oncept® is currently only available to veterinary oncology specialists. If your pet was diagnosed with oral melanoma, your regular veterinarian will need to refer you to a specialist in order to get your dog vaccinated. The vaccine is only licensed for dogs that already have melanoma, and cannot be given as a melanoma preventive.