Oral Tumors in Dogs – An Overview

What are oral tumors?

Like us, dogs can develop oral masses. Some will grow slowly and won’t spread to other locations (benign), while others will spread to different areas of the body causing great harm (malignant).

Benign oral tumors generally start in the periodontal ligament, which is located in the tooth socket. The most common types of oral tumors are called peripheral odontogenic fibromas (POFs). The acantomatous ameloblastoma is a more aggressive form of benign tumor which can be locally destructive.

POF   Acanthomatus ameloblastoma

The most commonly diagnosed malignant tumors are oral melanoma, followed by squamous cell carcinoma and fibrosarcoma.   
                                     Malignant melanoma  
Spindle cell tumor         Plasma cell tumor

How are oral tumors caused?

Although the exact cause is unknown, cancer is often the culmination of many factors including heredity, diet, and environment.

Some animals have a greater tendency (genetic susceptibility) to develop cancer. Large dog breeds, for instance, tend to be more susceptible to cancers than smaller breeds, and often for specific types of cancers.

The masses occur as a result of the affected, mutated cells which upset the normal regulation of cell death and replacement. They do this by activating growth-promoting oncogenes (cancer genes), inactivating suppressor genes and altering the genes that regulate normal, programmed cell death (apoptosis).

How will these tumors affect my dog?

Tumors form as swellings on the gums around the teeth and on the hard /soft palates. They frequently ulcerate and bleed and may become secondarily infected. Clinical signs may include bad mouth odor, drooling, difficulty eating, displacement or loss of teeth, and facial swelling.

How are these tumors diagnosed?

If you notice a swelling in your dog’s mouth, you should contact your veterinarian. The veterinarian can usually tell from looking into the mouth if it is a problem that requires immediate attention.

An accurate diagnosis of oral tumors requires microscopic examination of tumor tissue. Cytology, the microscopic examination of small cell samples, can occasionally be used to diagnose these tumors.

For a definitive diagnosis, prediction of behavior (prognosis) and assessment of the completeness of a tumor removal, veterinarians will rely on the results of a surgical microscopic examination of tissue (histopathology). Your veterinarian will submit either a small part of the mass (biopsy) or the whole mass to a laboratory, where a veterinary pathologist will examine and diagnose the lesion. If your veterinarian submits the entire mass, the pathologist may be able to indicate whether the cancer has been completely removed.

"An accurate diagnosis of oral tumors requiresmicroscopic examination of tumor tissue."

What types of treatment are available?

Surgical removal is the standard treatment for all oral tumors. If the tumor is invasive, it may be difficult to remove completely, and it may be necessary to remove a large piece of the jawbone (hemimaxillectomy or hemimandibulectomy). Most dogs respond well to this surgery. If your dog requires one of these complex and extensive surgeries, your veterinarian may refer you to a specialist at a veterinary referral center. (www.avdc.org). Melanomas are also treated with a vaccine after surgery.

Surgical site used to remove the tumor    Appearance after removal of left lower jaw to treat melanoma)

How will I know how these tumors will behave?

The histopathology report indicates how the tumor is likely to behave. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (distant spread) and, if the entire mass was submitted for examination, will usually assess the completeness of excision.

"The histopathology report indicates how the tumor is likely to behave."

When will I know if the cancer is permanently cured?

Benign tumors rarely recur if the cause of the proliferation and inflammation is removed. A few of the most active ones may regrow and require more extensive surgery. This may be indicated in the histopathology report.

Are there any risks to my family or other pets?

No, these are not infectious tumors. They are not transmitted from pet to pet or from pets to people.

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