Mouth Cancer in Dogs

Causes, Treatment, and Prevention

Dog mouth close up.

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Mouth cancer generally describes any kind of cancer that affects a dog's mouth. All dogs are at risk for mouth cancer, particularly in their senior years, but some breeds are more likely than others to develop it due to an unfortunate genetic predisposition. The signs may include swelling, bleeding, loose teeth, or a foul oral odor. Of course, these are symptoms of other periodontal conditions as well, so a veterinary diagnosis is critical.

What Is Mouth Cancer?

Mouth cancer is not one type of cancer; it refers to the location where cancer originates (cancer is the abnormal growth of cells within the body). Several different types of mouth cancer can occur in dogs, but melanoma, squamous cell carcinoma, and fibrosarcoma are the most common.

Symptoms of Mouth Cancer in Dogs

Mouth cancer can go unnoticed for some time, but the appearance of any of the following signs warrants a veterinary consultation as soon as possible.


  • Drooling or an increased salivation
  • Facial swelling
  • Bad breath
  • Face or mouth pain when chewing or being touched
  • Difficulty eating or drinking
  • Loose teeth 
  • Blood coming from the mouth
  • Visible mass in the mouth
  • Enlarged lymph nodes in the neck

A visible mass or tumor in the mouth is an obvious abnormality that may indicate the presence of cancer, but other signs may resemble dental diseases, such as drooling, bad breath, a loose tooth, or difficulty chewing. Periodontal disease is much more common than cancer, but both require treatment and carry better prognoses when caught early.

Lymph node enlargement may occur as mouth cancer progresses, indicating the body's immune response and the possible spread of the disease.

Causes of Mouth Cancer

There is no definitive cause of mouth cancer in dogs, but genetic factors appear to be involved in many cases. In general, male dogs and dogs with heavily pigmented gums, especially small dogs, appear to be at a higher risk of developing mouth cancer.

Some dog breeds are more likely than others to develop mouth cancer for reasons that researchers don't fully understand. These include:

Additionally, a dog that has parents with mouth cancer may be at a higher risk for developing the disease since it is likely that there is a genetic component to its development.

Diagnosing Mouth Cancer in Dogs

If you suspect your dog has mouth cancer, your veterinarian will recommend certain tests, beginning with a physical examination. The mouth will be thoroughly examined (some dogs may require sedation for this to occur, especially if the mouth is in pain).

If a mass is located in the mouth, then a fine needle aspirate or biopsy of the mass in the mouth will be recommended to identify the presence of cancer cells and identify the type of malignancy. An ultrasound, CT scan, or MRI may also be recommended once the cancer is diagnosed.

Bloodwork and X-rays will be performed to assess your dog's overall health and organ function, as well as to look for signs of cancer elsewhere in the body.


Surgery may be recommended to remove most or all of the mass, but this is not always possible. Chemotherapy or radiation may then be options based on the type of cancer, degree of progression, and financial considerations; otherwise, your dog's symptoms will be managed until its quality of life is compromised.

Prognosis of Dogs With Mouth Cancer

Some cancers spread quickly while others do not, so the treatment and prognosis of your dog's mouth cancer will depend on the type of cancer it has.

How to Prevent Mouth Cancer

Since the cause of mouth cancer is not fully understood, it is not possible to prevent it from developing in your dog. The best way to prevent mouth cancer at this time is to be sure not to breed a dog that has been diagnosed with cancer. This may help decrease the likelihood of a dog passing the genes that promote mouth cancer to offspring.

Types of Mouth Cancer in Dogs

The three most common types of cancer that affect dogs' mouths include the following:

  • Melanoma: Oral melanoma is the most common type of mouth cancer diagnosed in dogs and can spread into the bone.
  • Squamous cell carcinoma: Oral squamous cell carcinoma is the second most common type of mouth cancer in dogs and affects the outer layer of the tissues in the mouth.
  • Fibrosarcoma: Oral fibrosarcoma comes from the fibrous tissues in the mouth but can spread to neighboring tissues in the oral cavity.
Article Sources
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  1. Dobson JM. Breed-predispositions to cancer in pedigree dogs. ISRN Vet Sci. 2013;2013:941275.