Immunotherapy uses the body's own immune system to identify and kill tumor cells. Since melanoma is an antigenic tumor, many
studies have evaluated immunotherapy as a treatment. Tumor regression occurred in five of 13 (38%) dogs treated with human
recombinant interleukin-2 and tumor necrosis factor alpha, showing that immunotherapy can have anti-tumor effects.51,52
Another approach to immunotherapy is tumor vaccines. These vaccines are not preventive but therapeutic and work by stimulating
the immune system to recognize the malignant cells. One such investigational vaccine, an allogeneic whole-cell tumor vaccine
that expresses human glycoprotein 100, developed at the University of Madison-Wisconsin was used in 34 dogs (25 with oral
melanoma, eight with nail bed melanoma, and one with cutaneous melanoma) with bulky disease.53 The overall response rate was 17%, with a tumor control rate of > 6 weeks of 35%. As with chemotherapy, responses in dogs
with macroscopic disease lend support to the investigation of this therapy in dogs with microscopic disease.
A xenogeneic vaccine that uses human tyrosinase plasmid DNA (Canine Melanoma Vaccine, DNA—Merial) has a conditional license
for use in dogs with stage II or III oral melanoma in which local disease control has been achieved.54 The targeted antigen of this vaccine is the tyrosinase glycoprotein, which is involved in melanin production and, thus,
found in all melanoma cells. Limited data are published in regard to dogs with melanoma treated with this vaccine. In nine
dogs with measurable disease (five with oral melanoma, three with nail bed melanoma, and one with intraocular melanoma), with
tumor stages ranging from II to IV, a MST of 13 months was achieved with the vaccine, which was well-tolerated.55 The expected survival time for stage II to IV oral melanoma patients treated with surgery alone ranges from two to five
months.23,36,37 The vaccine is given intramuscularly once every two weeks for a total of four treatments, with booster vaccinations recommended
every six months, and it is available only through veterinary oncologists or internists.54 Ongoing studies of clinical patients treated with the vaccine will clarify the role and benefit of this new therapeutic.
The diagnosis and staging of oral malignancies is fairly straightforward. Early detection can be a great advantage in the
treatment of all the tumor types, as small size improves resectability and, in dogs with melanoma, decreases the likelihood
of early metastatic spread. Local disease is usually the cause of death in nontonsillar squamous cell carcinoma and fibrosarcoma,
while metastatic spread and local disease are both concerns in dogs with tonsillar squamous cell carcinoma and melanoma. Prognosis
may be predicted by the tumor's type, size, location, and stage at diagnosis. Multimodality therapy that can include surgery,
radiation, chemotherapy, and immunotherapy may be applied with varying success, depending on tumor type and location. Many
dogs with oral tumors can be successfully managed with appropriate care.
Virginia J. Coyle, DVM
Laura D. Garrett, DVM, DACVIM (oncology)
Department of Veterinary Clinical Medicine
College of Veterinary Medicine
University of Illinois
Urbana, IL 61802
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