by Edwin Brodsky, DVM, Diplomate ACVIM (Oncology)
The Melanoma Vaccine
Oral melanoma is the most common malignant oral tumor in dogs. Oral melanomas are both locally aggressive and systemically aggressive (up to 80% metastatic rate). Initial work-up for oral melanomas should include a minimal data base (CBC, chemistry, and urinalysis), lymph node evaluation with cytology or biopsy, three-view chest radiographs and biopsy confirmation of the oral melanoma.
Initially, local control is paramount for non-metastatic oral melanomas. Local treatments for oral melanoma consist of surgical removal, plus or minus radiation therapy. Radiation therapy may be necessary for dogs with oral melanomas when surgery is not able to be performed based on the size and location of the tumor or if surgery was unable to obtain clean margins, leaving behind microscopic melanoma. Radiation therapy is generally well tolerated with many dogs having minimal side effects. Some dogs may experience oral mucositis (inflammation of the lining of the oral cavity), however, most of the time this inflammation is mild and resolves with minimal supportive care, such as anti-inflammatory and pain medications. If the oral tumor is not adequately controlled with surgery or radiation therapy, the local effects of the tumor (oral pain, difficulty eating, and oral bleeding) will likely result in quality of life issues prior to the melanoma metastasizing to other locations.
Once a treatment plan has been formulated to control the local tumor, the next focus is trying to curtail the spread of the oral melanoma. When a tumor has a high metastatic rate, chemotherapy is generally used to help prevent or slow down the rate of metastasis. Unfortunately, oral melanoma is considered a chemoresistant tumor.
However, melanoma is considered to be an immunogenic tumor. This means that we can stimulate the body’s immune system to help fight off the cancer. Over the years, a variety of different immunostimulants have been used for the treatment of oral melanoma. Currently, the most effective immunotherapy available is the melanoma vaccine. The melanoma vaccine is not a preventative vaccine – like puppy vaccines. The melanoma vaccine is a therapeutic vaccine – it is used when a dog actually has melanoma. The melanoma vaccine is a human tyrosinase DNA vaccine. The vaccine uses human DNA for the enzyme tyrosinase, which is the rate limiting enzyme in melanin synthesis, to stimulate an immune response against cells that contain the enzyme. Melanin synthesis is generally limited to melanocytes – the cells which oral melanoma is derived, thus the vaccine is very specific for melanoma. Human DNA is used because it was found that using a foreign specie’s DNA was more effective in stimulating an immune response as compared to using the same specie’s DNA. The vaccine is safe with minimal side effects and was found to be effective in prolonging survival times in dogs with oral melanoma. The melanoma vaccine is considered to be most effective when the local tumor has been controlled with surgery and/or radiation therapy. The melanoma vaccine is not considered a substitute for surgery or radiation therapy when treating the problem of local disease progression.
Edwin Brodsky, DVM, Diplomate ACVIM (Oncology)
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006