Canine Melanoma: A Common, Aggressive Malignancy

Melanoma is an aggressive cancer arising from pigment-producing cells, accounting for 7% of canine tumors with certain breeds at higher risk. The most common form is oral melanoma, which affects the mouth and gums, and has the potential to metastasize. Cutaneous melanomas can also occur but are less common than oral melanomas and are often benign. Treatment typically involves surgical removal followed by radiation therapy for local disease control as well as systemic therapy given the metastatic potential. Prognosis varies based on location and stage, with median survival around 17-18 months for stage I oral melanoma post-surgery down to 3 months for stage III, but dermal and ocular forms can have better outcomes with early intervention.

While melanoma is typically seen in older dogs, certain breeds are considered at higher risk, including Chow Chows, Golden Retrievers, Miniature Poodles, and Spaniels.

Oral melanoma, which affects the mouth and gums, is the most common oral tumor in dogs and has a moderate potential to spread (metastasize) to other parts of the body, such as lymph nodes and lungs. The second most common location for melanoma is the nail bed (subungual), occurring in 15-20% of cases and similarly posing a risk of metastasis to lymph nodes.

Treatment Options

The treatment approach for canine melanoma depends on the type, location, and stage of the cancer. For oral melanomas, surgical excision is often recommended, followed by radiation therapy and systemic treatment to address any potential metastasis to other organs. Carboplatin is an injectable chemotherapy that is often considered and is typically well-tolerated but can cause gastrointestinal upset and has a poor success rate. The melanoma vaccine, Oncept, is a common treatment option for oral melanoma that is designed to stimulate the patient’s immune system to target remaining melanoma cells.

Canine malignant melanoma, especially oral lesions, ranks among the most frequently submitted tumors for DNA sequencing with FidoCure. The increasing number of sequenced cases has revealed common mutations and pathways that could benefit from targeted therapies. These targeted treatments are often considered following or alongside traditional interventions such as surgery, radiation, and/or the melanoma vaccine.

Dermal melanomas confined to haired skin can be cured with complete surgical removal, but a biopsy report following surgery can determine if additional therapy is required. Ocular melanomas are typically treated with enucleation (surgical removal of the eye) or, in some cases, radiation therapy.

Prognosis and Prevention

The prognosis for canine melanoma varies depending on the type, location, and stage of the cancer at the time of diagnosis. Dermal melanomas have a more favorable prognosis, especially if caught and treated early. Ocular melanomas can also be associated with a better prognosis, particularly if the tumor is confined to the eye and treated promptly.

The ability to sequence canine melanomas has led to the identification of common mutations that may add valuable prognostic information. Damaging alterations to the important tumor suppressor gene, PTEN, are common in canine melanomas and have often been associated with poor prognosis in human malignancies.

While there is no guaranteed way to prevent melanoma in dogs, regular veterinary check-ups and prompt examination of any new or changing skin lesions or oral masses are crucial for early detection and intervention. Additionally, protecting dogs from excessive sun exposure and avoiding potential carcinogens may help reduce the risk of developing melanoma.

For the most accurate prognosis and treatment recommendations for your dog with melanoma, consult your veterinarian or a veterinary oncologist. They can provide personalized guidance based on your dog's specific case, considering factors such as cancer stage, grade, tumor location, and concurrent health issues.