Downeast Dog News


By Dr. Gail Mason, DVM, MA, DACVIM | Feb 01, 2021

Cancer of the oral cavity (mouth) is relatively common in dogs. Although some tumors of the mouth are benign, there are several malignant tumors that can affect our pets. The most common malignant tumors in dogs are malignant melanomas, squamous cell carcinomas, and fibrosarcomas. Less commonly, osteosarcoma, chondrosarcoma, anaplastic sarcoma, and multifocal lobular osteosarcomas can occur in the oral cavity. One biologically benign oral tumor of note is an acanthomatous ameloblastoma (“epulis”). These common tumors grow slowly but cause local destruction and pain of the jawbone over time.


Most often the owner notices a mass in the dog’s mouth. This can be located along the gums, jaw, lips, cheek, or on the hard palate. Other symptoms include a foul odor from the mouth (halitosis), drooling, loose teeth, blood-tinged drool, or difficulty eating/chewing.


A fine-needle aspirate (FNA) is a simple, in-office procedure that can result in an accurate diagnosis over 90% of the time. However, because some oral tumors are inflamed, infected, or necrotic, a tissue biopsy may be needed for confirmation. A tissue biopsy is valuable in not only confirming a diagnosis, but also yields important information about the tumor’s expected biological behavior. This is key since oral tumors vary considerably in their tendency to metastasize to other sites in the body.


The term “staging” describes additional diagnostics used to determine the extent of the disease in a patient. Such tests may involve sampling of the lymph nodes closest to the oral tumor and thoracic radiographs (chest x-rays). Advanced imaging using a high-definition CT scanner is extremely useful.

A CT scan can reliably determine the extent of the primary tumor, the likelihood of spread to adjacent lymph nodes, and is able to detect even small metastatic lesions in the lungs. The scan provides invaluable information to both the surgeon and the oncology team to create the optimal treatment plan for the patient.


If determined to be feasible, surgical removal of the primary tumor is the most economical, expeditious, and potentially curative treatment. Large tumors or those that have invaded the bone below them may require removal of part of the jawbone in order to obtain adequate tumor-free (“clean”) margins. Although this type of surgery may sound daunting, it can be extremely successful and rewarding in the hands of a skilled surgeon. The rich blood supply to the mouth aids in rapid healing of most surgeries. The cosmetic and functional results are good to excellent. Additionally, the source of the dog’s pain is eliminated. If the pathologist determines that the malignant tumor has not been removed in its entirety, either a second surgery to remove additional tissue or radiation therapy to the surgery site may be recommended. Radiation therapy is also indicated for tumors that are too large to be completely removed. While the term “radiation therapy” conjures up negative images, it is important to realize that dogs tolerate this therapy well and do not experience “radiation sickness” as humans may.

Follow-up Treatment

If the malignant oral tumor has been completely removed and it has low biological activity, then no further treatment is generally required or recommended. One exception is osteosarcoma, which is a primary bone tumor. Additional treatment with a chemotherapeutic (carboplatin) can be beneficial in extending patient survival times.

Oncept® Melanoma Vaccine

Malignant melanomas carry the highest risk for metastatic disease in dogs with oral tumors. Chemotherapy has a less than 20% response rate. Oncept® is a human DNA, anti-melanoma vaccine which induces the patient to produce antibodies against an enzyme that melanomas need to thrive. The vaccine is very safe and can extend the remission time or potentially effect a cure in over 40% of oral melanoma patients. Its use requires that the primary tumor be removed at least to the level of only microscopic disease.


The overall prognosis for any one patient with an oral tumor depends on tumor type, tumor size at the time of diagnosis, clinical stage of disease, biological activity of the tumor, and treatment selection.

Median Survival Times:

• Malignant melanoma 5-17 months

• Squamous cell carcinoma 9-26 months (non-tonsillar)

• Fibrosarcoma 10-12 months

• Ameloblastoma indefinite

Primary care veterinarians can collaborate with specialists to determine the best treatment plans for a successful outcome and quality life extension.


Dr. Gail Mason, DVM, MA, DACVIM

Portland Veterinary Emergency & Specialty Care, Staff Internist