Canine Subungual (Nail Bed) Melanoma

Melanoma is a common tumor in dogs and may occur in the mouth, skin, toes, and eyes. These tumors commonly occur in Poodles, Dachshunds, Scottish terriers, Golden retrievers, Schnauzers, and Rottweilers. The behavior of the tumor depends on the location and grade.

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Subungual (nail bed) melanoma is uncommon in dogs but represents one of the more frequently identified nail bed disorders. Subungual melanoma may metastasis in approximately 1/3 to 1/2 of dogs, and the regional lymph nodes and lungs are the most commonly affected sites. Surgical removal of the tumor requires amputation of the affected nail, and only a small percentage of tumors will recur locally at the surgery site post-op.

Treatment consists of surgery to remove the primary tumor followed by immunotherapy. Surgery is the mainstay of treatment but surgery alone has been shown to not completely cure all dogs in that many develop metastatic disease within several months post-op. Because of this we often follow up with immunotherapy (vaccination) to prevent and kill any systemic spread of cancer. In cases where the tumor was not completely removed radiation therapy can kill residual disease at the initial site of surgery. This helps to provide good local control, but dogs still need to be followed with immunotherapy because of the aggressive nature of this cancer.

Recently a DNA-based vaccine has been approved by the USDA to treat canine melanoma. The vaccine is administered into the muscle of dogs by using an air-compressed system which contains a gene for human tyrosinase (which codes for protein specific to melanoma cells). The protein made by the human gene is considered “foreign” and the dog’s immune system recognizes it as such and mounts an immune response against it. The vaccine, therefore, allows a dog’s own immune system to recognize melanoma cells as foreign and will mount a response against the melanoma cancer cells. Studies have noted excellent responses in dogs with their survival extended by years in many cases. What we have found is that the vaccine works best when there is complete local control with all residual local tumor removed by either surgery or radiation therapy. The vaccine involves 4 treatments on an every other week basis with a booster every 6 months.

The prognosis for subungual melanoma is cautiously optimistic. Survival can be measured in years for dogs treated aggressively that have not experienced metastasis of the cancer.