Mouth Cancer in Dogs

Dog mouth close up.

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Cancer isn't a word anyone likes to hear, but there are several different kinds of it that can occur in dogs, including mouth cancer. All dogs are at risk for mouth cancer but some are more likely than others to develop it. While it may not be as common as some other kinds of cancer, knowing how to recognize the potential signs of mouth cancer, what dogs are at higher risk for it, and what can be done about it can help you keep your dog as healthy as possible.

What Is Mouth Cancer?

Mouth cancer is not actually a type of cancer but rather the location that the cancer originates, and cancer is the abnormal growth of cells within the body. There are several different types of mouth cancer that can occur in dogs but three types are seen more often than others:

  • 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.

Signs of Mouth Cancer in Dogs

  • Drooling or an increased salivation
  • Swelling of the face
  • Weight loss
  • Bad breath
  • Face or mouth pain when chewing or being pet
  • Difficulty eating or drinking
  • Food falling out of the mouth
  • Loose teeth 
  • Blood coming from the mouth
  • Visible mass in the mouth
  • Enlarged lymph nodes in the neck

Mouth cancer can go unnoticed for some time but there are several signs of this disease that you can look for. Drooling or excessive salivation along with food falling out of the mouth, bad breath, and difficulty eating or drinking may be initial signs of mouth cancer. Next, weight loss, blood coming from the mouth, pain when chewing or being pet on the face, and lymph node enlargement may be seen as the disease progresses. Occasionally you may also see facial swelling, a visible mass or tumor in the mouth, and even loose teeth.

Causes of Mouth Cancer

No one knows what causes mouth cancers in dogs but genetics are the most likely cause. With more research, more knowledge may become available but in most dogs with mouth cancer, the cause is never known.

Diagnosing Mouth Cancer in Dogs

If you suspect your dog has mouth cancer, your veterinarian will perform a full physical examination. The mouth will be thoroughly examined but some dogs may require sedation for this to occur. Bloodwork, a urinalysis, 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. A fine needle aspirate or biopsy of the mass in the mouth will be recommended to be obtained in order to see what kind of cancer is present microscopically. An ultrasound, CT scan, or MRI may also be recommended once the cancer is diagnosed.


Surgery may be recommended to remove most or all of the mass but this is not always possible. Chemotherapy may then be an option for your dog but otherwise your dog's symptoms will be managed until its quality of life is compromised. Some tumors 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 difficult 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 it. This may help decrease the likelihood of a dog passing the genes that may cause mouth cancer to its offspring.

Risk Factors for Developing Mouth Cancer

Some dogs are more likely than others to develop mouth cancer. In general, male dogs and dogs with heavily pigmented gums, especially small dogs, appear to be at a higher risk of developing mouth cancer but there are also specific breeds that are more likely than others to be affected. These include the following:

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.

Article Sources
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  1. Dobson JM. Breed-predispositions to cancer in pedigree dogs. ISRN Veterinary Science.

  2. Dobson JM. Breed-predispositions to cancer in pedigree dogs. ISRN Veterinary Science.