Finding and treating oral melanoma, squamous cell carcinoma, and fibrosarcoma in dogs - Veterinary Medicine
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Finding and treating oral melanoma, squamous cell carcinoma, and fibrosarcoma in dogs
The three malignancies most likely to occur in dogs' mouths can have devastating local or metastatic effects if not identified and treated quickly. Review how surgery—in conjunction with radiation, chemotherapy, or vaccination—may increase your patients' survival times.


VETERINARY MEDICINE


Immunotherapy

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.

SUMMARY

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

REFERENCES

1. Liptak JM, Withrow SJ. Oral tumors. In: Withrow SJ, Vail DM, eds. Withrow and MacEwen's small animal clinical oncology. 4th ed. Philadelphia, Pa: WB Saunders Co, 2007;455.

2. Oakes MG, Lewis DD, Hedlund CS, et al. Canine oral neoplasia. Compend Contin Educ Pract Vet 1993;15(1):15-30.

3. Todoroff RJ, Brodey RS. Oral and pharyngeal neoplasia in the dog: a retrospective survey of 361 cases. J Am Vet Med Assoc 1979;175(6):567-571.

4. Dorn CR, Priester WA. Epidemiologic analysis of oral and pharyngeal cancer in dogs, cats, horses, and cattle. J Am Vet Med Assoc 1976;169(11):1202-1206.

5. Cohen D, Brodey RS, Chen SM. Epidemiologic aspects of oral and pharyngeal neoplasms of the dog. Am J Vet Res 1964;25:1776-1779.

6. Bradley RL, MacEwen EG, Loar AS. Mandibular resection for removal of oral tumors in 30 dogs and 6 cats. J Am Vet Med Assoc 1984;184(4):460-463.

7. Brodey RS. A clinical and pathologic study of 130 neoplasms of the mouth and pharynx in the dog. Am J Vet Res 1960;21:787-812.

8. Dennis MM, Ehrhart N, Duncan CG, et al. Frequency of and risk factors associated with lingual lesions in dogs: 1,196 cases (1995-2004). J Am Vet Med Assoc 2006;228(10):1533-1537.


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