Overview

Oral squamous cell carcinoma (OSSC) is the second most common malignant (cancerous) oral tumor in dogs. These tumors often appear as pink or red irritated masses that easily bleed and can grow very large, causing dogs pain and discomfort. Surgical removal is often the treatment of choice. However, the tumors are often rapidly invasive to the surrounding structures of the mouth and bone and may require removal of portions of the jaw, radiation therapy, or may be too large to completely remove.                      

Cause

OSSCs are malignant tumors that tend to grow on the gums, under the tongue, or on the tonsils at the back of the mouth. Tumor appearances can vary in shape and color from pink, nodular, raised and irregular red masses to thickened and ulcerated plaques. Despite the size of the tumor’s external appearance, they often have an iceberg effect, meaning they are locally aggressive, and the extent of deeper tissue invaded by the tumor is often much larger.

There is no single known cause, breed predisposition, or risk factor for developing OSSC; it is likely a complex mix of environmental and genetic factors. Dogs of all ages may be affected by OSCC, but it occurs more commonly in older dogs and has been reported more frequently in Cocker Spaniels, Retrievers and Poodles.

Clinical signs

Because some of the signs can be similar, OSSC may be mistaken for periodontal disease early on in tumor growth. Since these tumors commonly invade the bone, dogs with OSSC are often painful. Signs associated with OSSC can vary depending on tumor location and size but may include any of the following:

• Bad breath
• Drooling with or without blood
• Facial swelling or asymmetry 
• Pain when opening the mouth 
• Decreased appetite
• Difficulty eating or swallowing
• Loose teeth
• Sneezing, nasal discharge, or bleeding. 
• Weight loss
• Enlarged mandibular lymph node

Diagnosis

An oral mass may first be noted at home or on a routine physical exam by your veterinarian. Your veterinarian may recommend a combination of tests to make a diagnosis or refer you to a specialist, and may include any of the following:

• Biopsy: a small piece of the tumor is removed and evaluated by a pathologist.
• Dental X-rays: imaging to determine the extent of bony involvement.
• CT scan: higher imaging if surgical removal is pursued

Additional testing to check for metastasis (spread of the cancer in the body) may include:

• Bloodwork and urinalysis
• Chest x-rays
• Abdominal ultrasound

• FNA (fine-needle aspirate) of lymph nodes

Treatment

Treatment options for OSSC may depend on the tumor's location, size, spread and the extent of invasion into local structures.

Surgery to remove the tumor is often the recommended treatment. However, due to OSSC’s invasive nature, it is not uncommon that a portion of the jaw may need to be removed to fully remove all the cancer cells. Radiation therapy may be recommended before or after surgery. Chemotherapy is uncommonly used alone for OSSC, but in some cases may be used combined with other treatments.

If surgery or radiation is not an option, supportive care can be temporarily provided to help keep your dog comfortable, but unfortunately will not slow the progression of tumor growth. Supportive care includes pain medications, nutritional support, and antibiotics if a secondary infection is present.

Outcome

The prognosis for OSSC varies depending on the size and location of the tumor. If all tumor cells are completely removed, surgical removal can be curative. Your veterinarian will recommend frequent rechecks to monitor for recurrence.

If the tumor is too large to be completely removed and cancer cells are left behind, recurrence is likely. Tumors that originate on the tonsil or underneath the tongue often have a worse prognosis and a higher likelihood of metastasis compared to tumors that are more forward (rostral) in the mouth, which tend to have a better prognosis.

Updated Aug. 2024