Melanoma is a very common type of cancer in dogs, but is rare in cats. Melanomas are normally classified by their location: oral, subungual (in the toe-nail bed), cutaneous (in the skin) or ocular (in or around the eye). Melanoma can be benign or malignant and generally occurs in older dogs (9 to 12 years). Regardless of type, melanoma tends to be locally invasive.
Certain breeds are predisposed to developing melanoma. These are the Doberman pinscher, Golden retriever, Gordon setter, Irish setter, Irish terrier, Chow chow, Chihuahua, Giant and miniature schnauzer, Boston terrier, Airedale terrier, Cocker spaniel, Boxer, Springer spaniel and Scottish terrier. This breed predisposition suggests an underlying genetic mechanism for melanoma in companion dogs.
Types of Melanoma in Dogs
Benign Skin Melanocytomas
Benign melanomas of the skin occur much more frequently in dogs than does the malignant form of this cancer. Cutaneous melanoma can develop anywhere on a dog’s skin, but often is first noticed on the head, in the mouth or on the front legs. The raised and often dark patches usually appear in isolation, but sometimes more than one may occur. Treatment for cutaneous melanoma may include a wait-and-watch approach or surgical excision of the mass and appropriate margins around the affected area. As this type of melanoma is usually benign, it has an excellent prognosis if caught and removed promptly.
Malignant melanomas in dogs are very aggressive and they spread rapidly throughout the dog’s body. This type of melanoma occurs most often in the dog’s mouth, under or around the toe-nails (subungual) and on the pads of the feet. These tumors also are seen on the abdomen and around the scrotum of dogs.
Malignant melanoma can present in a number of ways. Oral melanomas are uniformly malignant, locally invasive and highly metastatic – meaning that they spread commonly and rapidly. Regardless of where it appears, a malignant melanoma tumor can present as a raised pigmented or non-pigmented bump anywhere on the skin, or it can show up as a growth that looks like an infected sore. When this type of cancer develops under the nail or on the foot pad, the dog’s nearby toes usually will become swollen, the affected nails will slowly disintegrate and the dog normally will become lame.
Malignant melanoma should be treated aggressively, with surgical removal (with wide margins) as soon as possible after the neoplasia is diagnosed. Surgery may be followed by chemotherapy and/or radiation. Of course, your veterinarian is in the best position to advise you about an appropriate treatment protocol if your dog has developed this or any other type of cancer.