Melanomas and Mast Cell Tumors in Dogs (cont.)

Squamous Cell Carcinomas

These tumors are induced by exposure to the ultraviolet radiation in sunlight, and occur on lightly pigmented areas of the body, including the underside of the belly, trunk, scrotum, nail beds, nose, and lips.

One variety of squamous carcinoma appears as a hard, flat, grayish-looking ulcer that does not heal. Another appears as a firm red patch, and still another as a cauliflowerlike growth. There may be hair loss around the tumor because of constant licking.

Squamous carcinomas invade locally and metastasize at a late stage to the regional lymph nodes and lungs.

Treatment: Complete surgical removal is the treatment of choice. When this cannot be accomplished due to widespread involvement, radiation therapy can be used. Light-skinned dogs should avoid being in the sun at peak hours of UV exposure-generally 10 a.m. to 2 p.m.


Melanomas arise from melanin-producing cells in the skin. They are more common in Scottish Terriers, Boston Terriers, and Cocker Spaniels. These brown or black nodules are found on darkly pigmented areas of skin, particularly on the eyelids. Rarely, you will find an unpigmented melanoma. They also occur on the lips, in the mouth, on the trunk and limbs, and in the nail beds.

Melanomas on the skin are usually benign; those in the mouth are highly malignant. About 50 percent of nail bed melanomas are malignant and metastasize. Metastases occur in the regional lymph nodes, lungs, and liver.

Treatment: The melanoma must be removed surgically, along with a margin of normal tissue. Recurrence is common and difficult to treat. The outlook is extremely poor for melanomas in the mouth.