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Cancer of the oral
cavity is relatively common in dogs and cats. The annual incidence of oral
cancer in dogs is 20 per 100,000 and in cats 11 per 100,000. Although many
tumors of the mouth are benign, there are several significant malignant tumors
that affect our pets. Dogs are most commonly diagnosed, in decreasing
frequency, with malignant melanomas, squamous cell carcinomas, and fibrosarcomas.
Cats are most commonly diagnosed with squamous cell carcinomas followed by
fibrosarcomas.
Because of their
location, oral malignant tumors are often detected late in the course of the
disease process and have commonly progressed to Stage II at the time of
diagnosis. A Stage II tumor is one that is 2-4 cm in diameter with no evidence
of further spread.
Common
symptoms: Pets with oral tumors will
often have a history of pain while trying to chew or swallow food, food dropping
out of the mouth while eating, drooling, or not willing to eat at all.
Periodontal disease, bad breath, and tooth loss may also be noted. If lesions
are ulcerated, there may be blood-tinged saliva. By the time any abnormality
is noticed, the mass is likely to be large enough to be visualized in the oral
cavity.
How is the
diagnosis made?
Definitive diagnosis is based on the
histopathologic examination of a surgical biopsy of the mass. A fine needle
aspirate of the mass can be done initially to get a presumptive diagnosis, but a
biopsy is ultimately needed. Staging of the tumor is important before treatment
as it governs the treatment plan and helps determine the prognosis. Staging
describes if there is bone invasion, local lymph node involvement, or distant
metastasis and is evaluated through lymph node aspirates/biopsy and thoracic
(chest) radiography. The size of the tumor can be most accurately determined
when a pet is under general anesthesia. At this time skull radiographs, or
preferably a CT (computed tomography) scan can be performed to assess
invasiveness into the local tissues. A CBC, chemistry panel, and urinalysis
should be evaluated for concurrent disease or organ abnormalities related to
metastasis.
Malignant
Melanoma:
Malignant melanomas of the oral cavity
originate from the mucosa or gingiva. They often have brown or black
pigmentation, but can also be non-pigmented. Male dogs with heavily pigmented
mucosa such as German Shepherds and Cocker Spaniels may be more predisposed.
Malignant melanomas are characterized by rapid growth, local invasiveness, and
early metastasis to regional lymph nodes and lungs. Over half of the cases will
have bony invasion and lymph node metastasis at the time of presentation and
approximately 15% will have detectable lung metastasis. This tumor carries the
least favorable prognosis of all of the oral tumors.
Fibrosarcoma:
Fibrosarcomas arise from the gingiva or
connective tissue of the hard palate. They often appear firm and smooth with
nodules that may become ulcerated and can be seen on the upper jaw between the
canine and molar teeth. Dogs with fibrosarcomas are younger (average 7-8
years) than dogs with other oral malignancies (9-11 years). Fibrosarcomas tend
to affect large breed dogs. Fibrosarcomas are very locally invasive; therefore
recurrence after surgical excision is common. Metastatic behavior is variable.
Non-tonsillar
Squamous Cell Carcinoma (SCC):
In cats, these tumors most commonly arise from
the gingiva in front of the canine teeth and under the tongue. Other common
oral sites include the inside of the cheeks, hard palate, and tongue. They
appear as irregular, often ulcerated masses, or raised and inflamed plaques.
SCC is characterized by rapid growth, local invasiveness, but tends to be late
to metastasize. In dogs bony involvement is particularly common. Regional
lymph node metastasis is uncommon (5-10%) Non-tonsillar SCC is the least likely
of the oral tumors to metastasize to the lungs (10%), and when found in dogs,
have the most favorable prognosis when located in the rostral (front) portion of
the oral cavity. In contrast, treatment of cats with SCC is generally
palliative with poor success rates.
Tonsillar
Squamous Cell Carcinoma:
These tumors are more aggressive than gingival SCC because they are locally
invasive AND nearly all have metastasized to the regional lymph nodes at the
time of presentation. Potential for metastasis is quite high (>50%). These
masses appear as plaque or cauliflower-like lesions often affecting only one
tonsil. Tonsillar SCC and SCC occurring in the caudal (back) portion of the
oral cavity carry a poor prognosis.
Acanthomatous Ameloblastoma*:
The epulides are a group of benign tumors of
dental origin. Acanthomatous ameloblastoma is a member of this group.
Although technically “benign” (does not metastasize), it can be aggressive
locally by destroying underlying bone. Treatment with surgery and/or radiation
therapy is usually curative. Untreated, however, this disease can progress to a
point that affected patients can have significant pain in the jaw and are unable
to eat.
*Formerly called acanthomatous
epulis
Treatment of Oral Tumors:
Surgery:
Complete local excision with wide surgical
margins is recommended. Local recurrence is highly likely with inadequate
resection. Large tumors that have invaded the bone may require removal of part
of the jawbone in order to obtain “clean” (tumor-free) margins. Early
intervention with aggressive surgery can be curative in patients with non-tonsillar
SCC and fibrosarcomas. Surgery of small melanomas (e.g. < 2 cm) can result in
prolonged survivals.
Radiation therapy:
Some masses are too large to be completely
resected, therefore radiation therapy is often recommended in combination with
surgery. Some tumors are treated with radiation therapy before surgery in order
to attempt to shrink them down to a more operable size. Some patients are
treated post-operatively with radiation when the margins of the surgical
resection show tumor cells still present.
Chemotherapy: Chemotherapy
may be recommended for patients with more aggressive tumors (e.g. higher grade
tumors). In some patients, chemotherapy can provide short-term relief of pain
if the patient is considered to have an inoperable tumor or is a poor candidate
for radiation therapy.
Immunotherapy: Numerous
clinical trials involving the use of melanoma tumor vaccines have been conducted
or are underway. Several anti-melanoma vaccines have been evaluated and appear
to improve survival for certain patients with this disease. Although apparently
safe, efficacy is a concern. It appears that at least 30% of patients with
earlier stage disease may benefit from melanoma vaccination.
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