Early detection is key with oral cancer in small animals

Know what to look for

Figure 1

I don’t know whether the incidence of oral tumors in pets is on the rise nationwide, but I do know they comprise more of my caseload than ever before.

Oral tumors create a challenge for practitioners because dogs and cats tend to hide one until it is of great size. The larger the tumor, the more significant the surgery needed to remove it.

Of course, the aggressiveness of the surgery is dependent on tumor type; therefore an incisional biopsy is always helpful before deciding whether aggressive therapy is warranted.

The Epulides

Epulis (plural: epulides) is a general term for any gingival mass. The term also is used in veterinary medicine as a specific diagnosis, but newer terminology clarifies the situation.

A fibromatous or ossifying epulis—both are referred to now as peripheral odontogenic fibromas—can be large and may raise concern (Figure 1), but these tumors do not require radical excision.

Peripheral odontogenic fibromas are often pink, firm and non-ulcerated. They arise specifically from the gingival collar, often surrounding a portion of the tooth or the entire tooth. The ossifying version will have evidence of mineralization in its center when assessed with dental radiographs. Since these tumors are so very common in dogs, we will devote next month’s column to discussing their clinical manifestations and treatment.

Acanthomatous epulis—now referred to as acanthomatous ameloblastoma—is quite different from peripheral odontogenic fibromas. This tumor has not been documented to cause distant metastasis in dogs, but it is locally invasive and often causes lytic changes in the bone when shown on dental radiographs. The most common site of occurrence is the rostral mandible in the incisor or canine areas.

Curative-intent surgery with approximately 1-centimeter margins is recommended. However, if surgery is not a feasible option, or if owners choose not to pursue surgery, this is one of the oral tumors that can sometimes be controlled or cured through radiation therapy. Intralesional bleomycin injections are reported to have a beneficial effect in a small number of patients.

Squamous Cell Carcinoma

Figure 2: A benign melanocytic tumor on the edge of the left upper lip of a dog.

Feline oral SCC is a great example of the importance of early detection.

Feline oral squamous cell carcinoma (SCC) is a great example of the importance of early detection. Squamous cell carcinoma is locally invasive and rapidly growing, and therefore it is often difficult to obtain clean margins by the time it is detected in cats. Distant metastasis is possible, and a recent study suggests advanced cases have a higher rate of metastasis to regional lymph nodes than previously reported.

Of all the papers in the literature, one study by Marconato et al. has shown the most promise. It combined a multimodal approach to therapy involving surgery, radiation and chemotherapy. Because of the frequency of feline SCC in private practice, I will discuss this in a standalone column in the near future.

In comparison to cats, squamous cell carcinoma in dogs tends to be more amenable to obtaining surgically clean margins. I usually try to get at least a 1-centimeter margin around feline and canine SCC in all dimensions.

Osteosarcoma

Osteosarcomas (OSA) are not common in the oral cavity, but when they occur they look very different from those of the appendicular skeleton. Red, fleshy and readily bleeding, these masses grow quickly and tend to show lysis on radiographs rather than being osteoproliferative.

OSAs are considered to have a better prognosis when they occur in the oral cavity compared to appendicular osteosarcoma. However, radical resection is necessary and micrometastasis can occur. One study by Selmic et al. showed a median survival time for all dogs of 239 days. Dogs that underwent surgery had a median survival time of 329 days.

Melanoma

Figure 3: Large amelanotic melanoma on the lingual and buccal surfaces of the left mandible in a 10-year-old miniature poodle. Mandibulectomy, chemotherapy and immunotherapy have provided over two years of quality life with no evidence of metastasis thus far.

When I was in veterinary school in the mid ’90s, any oral tumor arising from melanocytes was considered malignant. However, a study by Esplin in 2008 suggested a subset of melanocytic tumors that are benign. These tumors are usually an incidental finding and are usually less than 1 centimeter in diameter. They are well circumscribed, pigmented and often occur on the mucosa of the upper or lower lips (Figure 2). Marginal resection appears to be adequate to prevent recurrence of these benign melanocytic tumors.

Malignant melanoma may be melanotic or amelanotic and requires radical resection. Although large tumors may have metastasized even if not noted on staging tests, acceptable survival times are sometimes achievable even with large tumors when pursuing multi-modal therapy (Figure 3).

Fibrosarcoma

Fibrosarcoma (FSA) occurs commonly on the maxilla of large-breed dogs and may be initially misinterpreted as a tooth-root abscess due to its tendency to cause a diffuse soft tissue swelling. However, FSA tends to palpate as a more firm swelling than swelling caused by an abscess.

Fibrosarcomas can create a challenge for pathologists since a histologically bland version of fibrosarcoma is clinically aggressive but looks very low grade under the microscope. If your biopsy diagnosis of “fibroma” or “fibrous tissue” does not correlate with what you are seeing clinically, ask the pathologist if a histologically low-grade, biologically high-grade fibrosarcoma is a possibility.

Hopefully this refresher on common oral tumors will prepare you to make your next diagnosis. Be vigilant for those oral tumors.

Recommended Reading

  1. Theon AP, Rodgriguez C, et al. “Analysis of Prognostic Factors and Patterns of Failure in Dogs With Periodontal Tumors Treated With Megavoltage Irradiation” J Am Vet Med Assoc, 1997;210:785-788.
  2. Kelly JM, Belding BA, et al. “Acanthomatous Ameloblastoma in Dogs Treated With Intralesional Bleomycin. Vet Comp Oncol, 2010;8:81-86.
  3. Bilgic O, Duda L, Sánchez MD, Lewis JR. “Feline Oral Squamous Cell Carcinoma: Clinical Manifestations and Literature Review” J Vet Dent, 2015;32(1):30-40.
  4. Marconato L, Buchholz J, Keller M, Bettini G, Valenti P, Kaser-Hotz B. “Multimodal Therapeutic Approach and Interdisciplinary Challenge for the Treatment of Unresectable Head and Neck Squamous Cell Carcinoma in Six Cats: A Pilot Study” Vet Comp Oncol, 2013;11(2):101-12.
  5. Selmic LE, Lafferty MH, Kamstock DA, Garner A, Ehrhart NP, Worley DR, Withrow SJ, Lana SE. “Outcome and Prognostic Factors for Osteosarcoma of the Maxilla, Mandible or Calvarium in Dogs: 183 cases (1986-2012)” J Am Vet Med Assoc, 2014;245(8):930-8.
  6. Esplin DG. “Survival of Dogs Following Surgical Excision of Histologically Well-Differentiated Melanocytic Neoplasms of the Mucous Membranes of the Lips and Oral Cavity” Vet Pathol, 2008;45:889-896.
  7. Ciekot PA, Powers BE, Withrow SJ, et al. “Histologically Low-Grade, Yet Biologically High-Grade, Fibrosarcomas of the Mandible and Maxilla in Dogs: 25 cases (1982-1991)” J Am Vet Med Assoc, 1994;204:610-615.

Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbins-ville, N.J. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News. 

Originally published in the September 2016 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today! 

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