Canine melanoma, one of the five most frequently diagnosed cancers, can develop in many places on a dog’s body. The way the tumor behaves varies with its location.
What is it? A canine melanoma arises in pigment cells on the skin (where, unlike human melanomas, it’s usually benign), in the mouth, in the nailbed (toenail) or footpads, or in the eye. While human melanomas are generally the result of too much sun, that doesn’t seem to be the case for dogs. Light-colored dogs are rarely affected by a melanoma; it’s more commonly found in dogs with dark coats and darkly pigmented skin. Oral melanoma (OMM) is the most common form and is often discovered during a routine examination or by the owner. It may appear on a dog’s gums, lips, tongue or hard palate.
Signs and symptoms.
On the skin or in the mouth, a melanoma usually (but not always) presents as a dark, raised mass. While a dog may not display symptoms early on, drooling, bad breath, bleeding and sometimes difficulty eating are among the signs. For the toenail or footpad, there may be swelling, the nail may become loose or the dog may show some lameness. Melanomas in the mouth or nail bed are the most aggressive.
How is it diagnosed?
Melanomas are diagnosed by fine needle aspiration (a quick, well-tolerated and inexpensive way for the vet to sample the mass) and/or biopsy. To refine the diagnosis and stage the cancer, the vet will take blood and urine samples, assess nearby lymph nodes, and X-ray or do a CT scan of the chest.
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How is it treated?
Regardless of where it appears, surgery to eliminate the primary tumor is the first and best treatment, followed by radiation or immunotherapy to slow down its spread. If the melanoma’s location rules out surgery, radiation or immunotherapy may be used on their own. Because melanoma tends to be unresponsive to it, chemo is rarely part of the treatment protocol.
Dogs who’ve had oral surgery, including removal of part of the upper or lower jaw bone, generally have good functional outcomes, adapting to the new jaw shape and learning how to eat as early as three days after surgery.
Radiation usually involves three to six treatments delivered daily or weekly; higher-than-standard doses seem to provide a better response. Immunotherapy uses the dog’s immune system to fight a cancer; Oncept, a DNA vaccine, has had promising results against oral melanomas. According to the literature, “dogs with stage II and III OMM treated with Oncept after surgical resection (with or without radiation therapy) had longer median survival times than dogs in the control group.” The vaccine, derived from DNA coded to the human gene for a melanocyte protein, tricks the dog’s immune system into attacking its own version of the same protein. It can also affect the dog’s skin cells, sometimes resulting in the dog having more gray fur after treatment.
Unfortunately, by the time a melanoma is recognized, it has often metastasized. In most cases following surgical removal of a melanoma, metastatic tumors in the lungs appear after a period of months. OMM is particularly quick to spread.
Are certain breeds predisposed?
While any dog can develop a melanoma, the following breeds are considered to be predisposed: Cocker Spaniels, Chow Chows, Scottish Terriers, black Labs, black Poodles, Golden Retrievers, Dachshunds, Dobermans, and Standard and Miniature Schnauzers.