How We Treat Malignant Oral Tumors in Cats and Dogs

Dogs and cats are frequently diagnosed with tumors of the oral cavity. This diverse group of cancers includes growths along the gingiva (gum), lips, tongue, tonsils, the bones and cartilage of the upper and lower jaws, and the structural components holding the teeth in place.

The most common oral tumors in dogs are melanoma, squamous cell carcinoma, and fibrosarcoma. In cats, the most common tumor is squamous cell carcinoma, above all others.

Oral tumors are typically diagnosed at a relatively advanced disease stage, when they are causing significant clinical signs for the patient. This can include drooling (with or without evidence of bleeding), halitosis (bad breath), difficulty eating and/or drinking, facial swelling, and/or signs of oral pain (pawing at the mouth or repeated opening/closing of the mouth.)

Oral tumors are very locally invasive, meaning they cause significant damage directly at their site of origin. Gingival tumors can invade the underlying bone, causing destruction of the jawbone and loss of support for associated teeth.

Certain oral tumors are more likely to spread to distant sites in the body. For example, oral melanoma has a higher chance of spreading to lymph nodes of the head and neck region via the lymphatic system, or spreading to the lungs via the bloodstream, whereas fibrosarcoma tumors rarely spread.

The treatment of choice for oral tumors in pets is surgical resection when possible. The feasibility of surgery will depend on several factors, including tumor size, patient size, the specific location within the oral cavity, and the degree of invasiveness to underlying tissue.

If surgery is performed, and the biopsy report indicates the edges of the submitted section are free from cancer cells, oncologists will consider such tumors having “adequate local control.”

If the report shows cancer cells abutting the cut edge of the tumor, regrowth of the tumor is possible, and therefore additional local control is recommended. Generally this entails radiation therapy.

When radiation therapy is performed following surgery, veterinary oncologists prescribe between 14-20 daily treatments administered over a several week period. This form of radiation therapy can lead to some significant, albeit transient, side effects in pets due to the incorporation of surrounding healthy tissue within the region being irradiated.

Side effects from radiation therapy in the oral cavity include ulceration of the oral tissue and skin and fur loss in the radiation field. A foul odor may develop as side effects occur in these areas and/or the tumor is destroyed by the radiation. This is usually temporary and decreases over time. If the eyes are included in the treatment field, the development of cataracts is possible.

Chemotherapy is variably effective for treating oral cancers in dogs and cats. Unfortunately, the most common oral tumors tend to be exceptionally resistant to this form of treatment. This means that when pets present with tumors that cannot be resected surgically due to size or location, the options are limited.

Oral melanoma in dogs is a special scenario that can be treated with immunotherapy, using a vaccine designed to target the patient’s immune system to attack residual cancer cells.

Some pets are diagnosed with oral tumors incidentally, meaning a growth is detected without the animal showing any clinical signs. Owners may visualize a mass in their pet’s mouth while they are panting or yawning. I’ve had owners detect a problem while their animal was lying on their back with their mouths open in a position where their tongue falls away from their bottom jaw.

There are no proven methods for preventing oral cancer in pets. However, earlier detection of disease would provide the best chance for long term survival. Taking a look in your pet’s mouth once a month could aid in diagnosing oral tumors prior to their causing clinical signs. This task is easier said than done, as many pets are not too happy about having their mouths fussed with.

A thorough oral evaluation should be part of every routine wellness exam for dogs and cats. Veterinarians also struggle with successfully peeking in the mouths of our patients, but we’re generally more experienced with the process and also have more of an idea of what to look for and what could be concerning. When in doubt, it’s generally very safe to administer a touch of a sedative to facilitate oral exams.

Oral tumors can also be detected during routine dental cleanings or while pets are undergoing anesthesia for an unrelated reason. Those procedures allow for a more thorough evaluation of the oral cavity, and every attempt should be made to capitalize on the degree of visualization possible while an animal is anesthetized.

There are several clinical trials and many ongoing research studies for animals with oral tumors. Veterinary oncologists are the best reference point for owners looking for further information regarding this type of cancer, especially with reference to determining a pet’s eligibility for novel therapies.

Owners can find additional information on oral tumors, their diagnosis, and treatment options on the website for the Veterinary Society for Surgical Oncology.