The saying among pathologists - "nothing good ever grows in the mouth of dogs or cats" - is more than just a reflection of our normal, gloomy perspective on life! Depending on the study, 75-90% of oral tumors in dogs (excluding gingival epulides) are melanomas, squamous cell carcinomas or fibrosarcomas. In cats, 60-75% are squamous cell carcinomas and most of the rest are fibrosarcomas. While there is some difference in behavior and therapeutic response depending on the specific tumor and its location, oral tumors in both species are locally invasive and osteolytic, have a very high frequency of local recurrence, and an almost equally high prevalence of eventual metastasis to local lymph node and to lung (unless we intervene with euthanasia). This dismal prognosis can be improved considerably, particularly in terms of the rapidity of local recurrence, by radical surgical excision, and/or by the use of radiation therapy.

Prognostic data for the various tumors are presented on the next page. A word of warning: these data are highly biased by the timing of diagnosis. Most come from referral institutions and thus reflect the post-surgical survival times for relatively advanced disease. With the growing popularity of dental examination, I suspect that we will be detecting these tumors much earlier. This may not reduce the eventual case fatality rate, but it should result in a much longer interval between surgery and euthanasia. Whether it will improve the cure rate or not is harder to predict.

What about adjunct therapies?
Based on available data, these are palliative rather than curative. About 80% of canine oral melanomas respond to a high dose radiation fractionated over three doses (days 0,7,21). In about half the cases, the oral tumor completely disappears but the prevalence of fatal distant metastasis is not affected. Even though eventual case fatality rates probably remain the same, the quality of life is greatly improved and the need for premature euthanasia because of locally destructive growth is greatly reduced. Irradiation of feline oral squamous cell carcinomas increases median survival time from 3-6 months to 12-14 months but does not result in cure.

Are there any "good" oral tumors?
Exophytic nodular growths along the gingiva usually are foci of gingival hyperplasia or one-type-or- another of epulis. Even though one type of epulis - acanthomatous epulis - requires fairly aggressive resection to ensure cure, none are life threatening.

Granular cell tumors are smooth nodular growths that bulge from the surface of the canine tongue. Their cell of origin remains controversial but at least some originate from Schwann cells of peripheral nerve. They are cured by excision and have no metastatic potential.

Plasmacytomas occur in mouth as yet another of their unusual site predilections that include ear canal, larynx, toe, prepuce and rectum! Although a few will recur because of initially incomplete excision in this difficult operative environment, they have no metastatic potential.

Squamous cell carcinomas are probably more manageable than the other oral malignancies, especially if detected early. Early tumors may not look proliferative: my records are full of mildly osteolytic lesions of tooth sockets or subgingival bone, or of non-healing sublingual ulcers in cats, that are identified on biopsy as squamous cell carcinomas. Many are well differentiated tumors that seem to progress only slowly, so early surgical intervention may offer a good chance for complete cure. The prospects for cure look better for dogs than for cats. As usual, the feline tumors seem inherently more aggressive despite a histologic appearance that is virtually identical to that of dogs. Part of the dismal prognosis relates to anatomy (you can't amputate much from a cat's tongue!), but there also seems to be a fundamental species difference. Those from the maxilla are particularly nasty, and a one-year survival with even the most determined therapy is the best you can offer. We may discover some new magic bullet, but realistic pessimism seems to be the watchword for now.

The tables below are summaries of available data; results from similar studies have been combined for ease of presentation. Please note the very small numbers under some headings, which make definitive prognosis virtually impossible.

PREVALENCE OF ORAL NEOPLASIA IN DOGS AND CATS IN ONTARIO*

POSTOPERATIVE BEHAVIOR OF GINGIVAL SQUAMOUS CELL CARCINOMAS IN DOGS

POSTOPERATIVE BEHAVIOR OF TONSILLAR SQUAMOUS CELL CARCINOMAS IN DOGS

POSTOPERATIVE BEHAVIOR OF ORAL MELANOMAS IN DOGS

POSTOPERATIVE BEHAVIOR OF ORAL FIBROSARCOMAS IN DOGS

POSTOPERATIVE BEHAVIOR OF GINGIVAL SQUAMOUS CELL CARCINOMAS IN CATS*

References:

1. Todoroff, R.J. and Brodey, R.S., Oral and pharyngeal neoplasia in the dog: a retrospective survey of 361 cases. J Amer Vet Med Assoc 175: 567-571, 1979.



2. Kosovsky, J.K., Matthiesen, D.T., Marretta, S.M. and Patnaik, A.K., Results of partial mandibulectomy for the treatment of oral tumors in 142 dogs. Vet Surg 20, 6: 397-401, 1991.



3. White, R.A.S., Mandibulectomy and maxillectomy in the dog: long term survival in 100 cases. J Small Anim Prac 32: 69-74, 1991.



4. Wallace, J. and Matthiesen, D.T., Hemimaxillectomy for the treatment of oral tumors in 69 dogs. Vet Surg 21, 5: 337-341, 1992.



5. Vos, J.H. and Van Der Gaag, I., Canine and feline oral pharyngeal tumors. J Vet Med 34: 420-427, 1987.



6. Schwarz, P.D., Withrow, S.J., Curtis, C.R., Powers, B.E. and Straw, R.C., Mandibular resection as a treatment for oral cancer in 81 dogs. J Amer Anim Hosp Assoc 27: 601-610, 1991.



7. Schwarz, P.D., Withrow, S.J., Curtis, C.R., Powers, B.E. and Straw, R.C., Partial maxillary resection as a treatment for oral cancer in 61 dogs. J Amer Animal Hosp Assoc 27: 617-624, 1991.



8. Salisbury, K.S., Richardson, D.C. and Lantz, G.C., Partial maxillectomy and premaxillectomy in the treatment of oral neoplasia in the dog and cat. Vet Surg 15, 1: 16-26, 1986.



9. Bradley, R.L., MacEwen, E.G. and Loar, A.S., Mandibular resection for removal of oral tumors in 30 dogs and six cats. J Am Vet Med Assoc 184: 460-463, 1984.



10. Bradley, R.L., Sponenberg, D.P. and Martin, R.A., Oral neoplasia in 15 dogs and 4 cats. Small Anim Vet Med Surg 1: 33-42, 1986.