A Review of Canine and Feline Oral Tumors

by Dr. Daniel T. Carmichael
(thank you to Jill Costigan for editorial advice)

A Review of Canine and Feline Oral Tumors

Key Points:

• There are a variety of neoplastic (cancerous) and non-neoplastic lesions that can be found in the oral cavities of dogs and cats. An accurate diagnosis is required to offer appropriate treatment recommendations
• Oral biopsy is a procedure that must be performed correctly to obtain an accurate diagnosis
• Regional lymph node evaluation is an important part of a complete diagnostic workup for oral malignancies

The oral cavity is a common site of malignant neoplasia in both the dog and the cat. Tumors of the oral cavity can be classified as odontogenic tumors (neoplasia arising from tooth-forming tissues), non-odontogenic tumors, or non-neoplastic lesions.

In dogs, the non-odontogenic tumors include the three most common malignant oral neoplasms: melanoma, squamous cell carcinoma, and fibrosarcoma. Odontogenic tumors, generally considered to be rare, are actually common if the odontogenic benign tumors are included. Non-neoplastic lesions, such as cysts, hyperplasia, and inflammatory or infections processes, present a varied set of pathologies and treatment recommendations.

Unfortunately, the vast majority of neoplasms found in the mouths of cats are malignant and carry a poor prognosis. Over 20 different types of cancer have been reported to occur in the oral cavity of felines, although only a few are observed commonly. Among the more common feline oral neoplasms are squamous cell carcinoma (SCC), fibrosarcoma, lymphoma, and malignant melanoma. In fact, SCC alone accounts for about 70% of all feline oral tumors. Neoplasia must be suspected in all lesions of the feline oral cavity where an obvious cause is not clear. Any swelling (soft tissue or bony) or abnormal appearance of tissue in the oral cavity must be considered suspicious for neoplasia. In one study, however, it was shown that one-half of the swellings in the lower jaw bone of cats were non-neoplastic. A common, but very subtle presentation of oral neoplasia is when a tooth can be extracted too easily. Common presenting signs for cats with oral neoplasia include: an obvious oral mass, excessive salivation, weight loss, halitosis, bloody oral discharge, and dysphagia.

Initial work-up for oral tumors in dogs and cats

The successful management of any oral tumor depends on an accurate histopathological diagnosis prior to definitive treatment. An accurate histopathological diagnosis requires a representative sample of the tumor and a pathologist well versed in oral pathology to evaluate it.

Prior to the biopsy procedure, the patient should receive a thorough physical and oral examination. The oral lesion should be carefully inspected and described in terms of its location, size, shape, presence of ulceration or necrosis, and additional associated findings such as loose teeth in the tumor area. The regional lymph nodes should be carefully palpated, and irregular enlargements or lack of mobility (suggesting tissue fixation) must be noted. Finally, a thorough physical examination of the entire patient should be performed to detect signs of distant metastasis or other problems Blood work (CBC and blood chemistry analysis), urinalysis, and chest x-rays are also indicated to complete a pre-biopsy workup.

Obtaining an oral biopsy

The recommended method for obtaining an oral biopsy sample is an incisional biopsy taken from the within the boundaries of the tumor so that no marginal tissue planes are violated by the biopsy procedure. The biopsy sample should be taken atraumatically to restrict exfoliation of neoplastic cells. In larger tumors, it is best to obtain multiple samples from different locations within the mass. Oral biopsy procedures should be performed under general anesthesia maintained with a cuffed endotracheal tube. At the time of biopsy, existing dental pathology should be addressed if possible. The area suspected of containing the neoplasm should be radiographed, ideally with intra-oral dental radiographs because of their superior detail.

At the time of oral biopsy, while the patient is under general anesthesia, radiographs and other diagnostic imaging (CT, MRI) can be performed.

Treatment: canine tumors

“Epulis”

The term epulis has been applied to a variety of oral tumors. The so-called fibromatous and ossifying versions of epulis are actually odontogenic fibromas (arising from periodontal ligament), and are curable with complete surgical removal. The so-called acanthomatous epulis, on the other hand, is actually a peripheral ameloblastoma and is very locally aggressive (but will not metastasize.) The “acanthonmatous epulis” can also be cured by surgical resection, but wide margins are necessary to obtain complete excision. This tumor is also radiosensitive as well as sensitive to localized chemotherapy, but surgical excision is generally considered the most appropriate course of treatment.

Oral malignancies

Non-odontogenic oral malignancies are best treated on a case-by-case basis based on the results of biopsy, lymph node analysis, and metastatic screening. Tumors that have already metastasized will obviously carry a poorer prognosis. Surgical excision remains the most frequently indicated and most practical method of treatment. In most cases, the ultimate goal is to cure the patient; this is achieved by adequate excision, tumor-free margins, and the absence of metastatic disease. If the extent of disease makes this impossible, palliative surgery can be performed to provide relief from symptoms for as long as possible.

The appropriate width of the surgical margins is paramount for success. The tumor type, size, and client expectations will determine if a marginal, en bloc, or radical excision is indicated. Client education is imperative. Clients must be informed of the possible complications, the esthetic consequences, and the long-term prognosis to avoid misunderstandings and surprises. Owners are often not aware of how good most dogs actually do following major resective surgery.

It is always beneficial to coordinate the efforts of the oral surgeon and an oncologist to offer the patient the most up-to-date treatment options for the best possible outcome. In some tumors, adjunctive therapy with radiation, chemotherapy, or immunotherapy can improve the odds of success following surgery.

Odontogenic tumors and cysts

Odontogenic tumors can present as soft tissue masses such as amelobastoma, or can also involve dental hard tissue, including enamel, dentin, cementum, and pulp. Some of the odontogenic tumors are known to invade bone, and for these tumors en bloc or radical excision is indicated.

Dentigerous cysts are often diagnosed in young adult dogs and commonly are associated with embedded or impacted teeth. Dentigerous cysts can occur in any breed, but are overrepresented in Brachycephalic breeds and are most commonly located just behind the mandibular canines involving with the first mandibular premolars. Any missing tooth, especially missing first mandibular premolar teeth in brachycephalic breed, should be radiographed and extracted if found impacted. The treatment for dentigerous cyst involves surgical debridement of the epithelial cyst-wall lining as well as removal of the offending tooth.

Non-neoplastic oral growths

Non-neoplastic oral growths are common in the dog and include such clinical entities as gingival hyperplasia, inflammatory lesions, and various types of cysts. It is imperative to accurately diagnose these with histopathological confirmation. Bottom line: all oral growths should be biopsied and definitive treatment should be rendered based on the results of that biopsy.

Treatment: feline tumors

Squamous Cell Carcinoma

Feline oral SCC is an extremely invasive and malignant neoplasm. Unfortunately, to date, there are no therapies, or combinations of therapies, that are substantially beneficial for feline oral SCC. The recurrence rate for cats with oral SCC treated with surgery alone (and/or with radiation therapy) is felt to be extremely high with a median survival time less than 6 months, and these authors believe a median survival time of 30 – 60 days is more likely. The exception to this are cats with extremely small oral SCC involving the lower jaw that may be able to undergo major oral surgery, however, it must be stated that even these cases can have recurrence in the face of histopathologically-determined “clean” margins. In addition, the use of radiation therapy as a sole treatment modality is also felt to be correlated with a median survival time less than six months, with a recent report documenting a median survival time of only 60 days with 3 large doses of palliative radiotherapy. Though relatively few reports exist on the sole use of chemotherapy for feline oral SCC, it too is generally felt to be minimally beneficial when used in this way. In fact, these authors believe that the use of single modality therapy for feline oral SCC should be discouraged unless the tumor is a small lower jaw SCC, or if the tumor is being palliatively treated with 3 – 6 large doses of radiation therapy.

The aforementioned lack of efficacy with single modality therapy in feline oral SCC suggests that multimodality therapy and/or novel therapies are necessary to make advances in the treatment of this aggressive cancer. Unfortunately, relatively few reports exist in the literature in this regard.

Fibrosarcoma

Fibrosarcoma (FSA) is the second most common tumor of the feline oral cavity. Approximately 10 – 20% of feline oral tumors are FSA. FSA generally occurs in older cats (median age 10 – 12 years), however, cats as young as one year of age and as old as 22 years have been reported. There does not appear to be any gender predisposition or oral cavity site predilection, however, most cats with oral FSA have their tumors starting in the gingiva.

Other than the above descriptive data, there is extremely little clinical information on cats with oral FSA. Most cats with oral FSA will present for the same problems as cats with oral SCC; however, cats with oral FSA invariably will have a mass effect at the primary tumor site. Non-ulcerated oral FSA invariably has a significant amount of hyperplastic epithelium overlying the tumor, and therefore, procurement of a deep incisional biopsy is recommended to best ensure a correct histopathological diagnosis.

Feline oral FSA are extremely invasive malignancies necessitating wide surgical extirpation. Though few reports exist concerning recurrence rates with feline oral FSA, minimal surgical removal generally results in recurrence. Unfortunately, aggressive surgical extirpation of these tumors with histopathologically determined “clean” margins likely results in recurrence in 20 – 30% of cases due to their incredibly invasive nature. The routine use of radiation therapy in cats with large bulky oral FSA is generally discouraged. However, the use of radiation may be beneficial in cases with incomplete surgical resection for feline oral FSA, or if the radiation is being used palliatively (3 – 6 large doses). Similarly, the use of chemotherapy in this disease is generally discouraged due to the relative chemo resistance of soft-tissue sarcomas. However, chemotherapy is occasionally used in cats with large oral FSA in an attempt to shrink the tumor for later surgical resection, or in cats with high-grade (and therefore greater chance for metastasis) oral FSA.

Fortunately, feline oral FSA are not generally very metastatic. Less than 10% of feline oral FSA cases will have metastasis at the time of presentation. Therefore, this tumor is best treated with locally aggressive therapies. In summary, feline oral FSA are incredibly invasive, but minimally metastatic tumors that can potentially be cured via aggressive local therapies including surgery and/or radiation therapy.

Other Tumors

Though rare, a variety of other diagnoses are on the differential list for feline oral neoplasia. These include lymphoma, osteosarcoma, melanoma, chondrosarcoma, granular cell tumors, fibropapillomas, hemangiosarcoma, ameloblastomas and fibromatous or ossifying epulides. The prognosis for cats with oral lymphoma or hemangiosarcoma is presently unknown because it is such a rare site of involvement, however, the use of local therapy (surgery and/or radiation therapy) and adjuvant chemotherapy would be recommended due to its aggressive local and systemic nature. The other tumors listed above would be generally thought of as locally aggressive, but minimally to non-metastatic tumors, suggesting that aggressive local therapy would have a high chance of being curative.