Mouth Cancer in Dogs: A Helpful Guide


Mouth cancer is a rare, but present—and potent—disease affecting dogs and their owners today. With no determined cause, mouth cancer in dogs has left even subject matter experts baffled.

As with any disease of its kind, keeping informed can help you decipher what to do should a tumor linger in your dog’s mouth, and even prevent it from progressing further.

Mouth Cancer in Dogs: The Two Types of Tumors

The good news? Not all tumors develop into dog cancer. There are two types of tumors that can develop in a dog’s mouth: benign, and malignant.



Benign tumors are considered non-cancerous growths and are normally well-defined at the edges. Being that they’re benign, these do not spread throughout the body, and are easier to remove through surgery.


Malignant tumors, on the other hand, are cancerous and tend to metastasize, or “spread” to the areas around them. This makes removal quite difficult.

The most common malignancies in a dog’s mouth are:

  • Malignant melanoma: Considered the most common type of mouth cancer in dogs, malignant melanomas are both invasive and spread rapidly, making surgical removal quite challenging. Additionally, this cancer spreads so fast that by the time symptoms are caught, it has most likely already reached other parts of the body.
  • Squamous cell carcinoma: This cancer is found in the mouth and throat, and can be painful. Caught early, the prognosis of treatment and recovery is normally good; otherwise, it can spread very quickly.
  • Fibrosarcomas: These tumors take on the shape of a cauliflower, similar to the squamous cell carcinoma, and don’t tend to spread until later in their development.
  • Acanthomatous ameloblastomas: Although these malignant tumors don’t tend to spread, they can be extremely aggressive and invasive of the surrounding tissues.

What Causes Mouth Cancer in Dogs?

Most modern veterinarians agree: there is no known cause for mouth cancer in dogs. The following are two theorized causes:

Inhaled Carcinogens

These cancer-causing substances may be inhaled by dogs as they sniff the ground, giving cancer-causing agents the opportunity to seize and affect otherwise healthy cells.

Ingested Carcinogens

A recent study discovered a possible link between certain commercial dog foods and mouth cancer. Chemical preservatives and pesticides utilized in dog food formula are suspected to be carcinogenic, but further evidence is needed.

Additionally, the following have been identified as risk factors for cancerous growths in dogs:

  • Dogs with darkly pigmented mucosa—the mucous membrane lining a dog’s mouth—are most prone to cancerous growths
  • Older male dogs are diagnosed with oral cancer more than younger dogs, or female ones


Signs and Symptoms of Mouth Cancer in Dogs

As with all forms of cancer, early detection will help increase the chances of treatment. As a pet owner, it is suggested to check your dog’s mouth regularly for the following:

  • Abnormal growths or lumps inside the mouth
  • Overgrown gums
  • Bleeding or other discharge
  • Visible sores or white lesions
  • Swelling in mouth

In addition, symptoms tend to include:

  • Indications of pain, including: pawing or rubbing at the face; chattering of the teeth, or not wanting to chew
  • Drooling
  • Difficulty eating: chewing and/or swallowing
  • Weight loss
  • Pain and tenderness of the gums or mouth
  • Halitosis (bad-smelling breath)

Diagnosing Mouth Cancer in Dogs

Be prepared to give a history of your dog’s health. Your veterinarian will perform a physical exam and take body fluid samples for laboratory analysis to check if your dog’s internal organs are functioning properly.

Your veterinarian will also conduct a biopsy, removing tissue from the lump for further microscopic examination. He or she will want to know how far the tumor has spread into the surrounding tissue, and in some cases, may even order further tests such as a chest or abdominal x-ray to see if it has metastasized.

Treating Mouth Cancer in Dogs

Because each case of cancer is so varying and unique in its characteristics, the treatment will depend on the size and growth of the tumor. The following have been found as the most effective treatments on smaller tumors:

  • Surgical removal
  • Freezing of the tumor material, known as cryosurgery
  • Radiation therapy at the site

If your dog’s tumor is too large to remove by these methods, radiation therapy and/or chemotherapy may be used. Although some dogs are cured when these treatments are used in tandem, this treatment is more often than not found to slow the growth. These aggressive treatments may also be supported by holistic therapies like herbal, mineral and vitamin supplements.

Dealing with cancer of any kind can be unsettling as a loving pet parent, but you are not alone. Through the proper education and treatment plan, your dog is better set up to live and love as you have so carefully cared for him.

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