Dog mouth open

There are two types of mouth cancers: benign and malignant

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Everything you need to know about dog's mouth cancer

By Dr Holly Graham BVMedSci BVMBVS MRCVS Veterinarian

Updated on the

Cancerous masses of the oral cavity, or mouth, make up a small proportion of tumorus affecting dogs. Read on to find out more about the causes, symptoms and treatments of mouth cancer in dogs.

Oral tumours are the fourth most common type of tumour in dogs, and are more common in males than females. There are many different types of tumour that can affect the mouth, some are benign (less aggressive and often harmless) but mouth cancers can be aggressive and malignant. The prognosis for mouth cancer depends entirely on the tumour type.

Two types of mouth cancer

There are two types of mouth cancer: benign tumours and malignant tumours.

Benign tumours

Benign tumours are usually tumours that are well-defined in tissues, affecting small areas of the body with a low chance of spread. Whilst these tumours might not cause problems around other parts of the body, they can cause problems locally. These tumours can often be removed with a low chance of recurrence, but this depends on their location and how large they are. Benign tumours pose a low threat to an animal, but lots still need to be removed due to irritation or an unsightly location. Benign tumours can sometimes be diagnosed from a needle biopsy, but for a confirmatory diagnosis many need full remove and histological analysis. Never assume a tumour is benign based on appearance, they can be sneaky!


Epulis are tumour commonly found in dogs. They are benign and affect the gum tissue around teeth. Epulis can be small, and affect single areas; or they can cover the majority of the gum in the mouth. Whilst they don’t spread to other areas of the body, they can grow large and cause problems with teeth and the gingiva of the mouth. You might notice swellings or excessive gum growth, drooling or bad breath. Epulis can become sore, and affect eating. These tumours more commonly affect brachycephalic dogs, dogs with squashed faces - like boxers and pugs. Depending on the severity and extent of the epulis, surgical removal is occasionally required.

Speak to your vet and always get any mouth masses checked out. It’s different to differentiate an epulis from a malignant tumour!

Malignant tumours

A malignant cancer is often nastier than a benign tumour. These tumours spread more easily, and cause more local damage to tissue. If diagnosed they may require extensive surgical intervention to remove, and may require more advanced investigation to check if they have spread to other areas. There are many different types of malignant tumour, and their treatment and prognosis depend on what tumour is diagnosed.

Squamous cell carcinoma

Oral squamous cell carcinomas are the second most common form of oral cancer, and the most common form to affect the tongue. Tumours are aggressive, but are slower growing than other forms of mouth cancer. Tumours can be difficult to eradicate completely because of their location. These tumours most commonly affect middle-aged dogs.

Your vet will want to assess whether the tumour has spread, and a combination of surgical removal and radiotherapy or chemotherapy may be advised if there is no indication that the tumour has spread to other sites in the body.


Fibrosarcomas are less common than squamous cell carcinomas, but are another malignant tumour with potential to spread to other organs. The tumours commonly affect local tissue in the mouth, but only around 30% spread to other regions of the body. These tumours are most commonly seen in large breed, middle-aged dogs. Surgical removal is the treatment of choice, if appropriate - but removal can be difficult.

Oral melanoma

Melanomas are the most common, and most aggressive form of oral cancer. These tumours are often black in colour due to the melanocyte cells that are affected. These tumours extend deep into tissues, and often invade underlying bone. Unfortunately these tumours have a poor prognosis, and most dogs with the condition live only a matter of months. If a tumour is confirmed to be a melanoma, it’s likely that imaging of the head and neck will be required to check how extensive the spread of the tumour is. Breeds that show a high incidence of melanoma include:

Oral osteosarcoma

Osteosarcomas arise from bone, and oral forms are less common than in legs or long bones. These tumours cause significant pain, and can be extremely challenging to treat. Excision is often only possible by removal of either the entire upper or lower jaw, and neurological damage may be permanent.

Causes of mouth cancer in dogs

There are no particular reasons identified as to why a dog may, or may not, develop cancer. Very few tumours have a single known cause, and many are often multi-factorial - or just bad luck. Some breeds seem to be predisposed to tumour development, and are at higher risk of being affected by tumours. There is likely a hereditary component, as well as environmental factors in the development of cancerous cells.

Symptoms of mouth cancer in dogs

Mouth cancers can present in many different ways. They can be vague and are often mistaken by owners for things like dental disease or infection. Regular checks of your dog’s mouth and teeth are essential to pick up any changes that might be concerning. Any new swellings or growths should be checked by a vet as soon as possible. But not all cancers are easy to detect as an obvious mass. The following other symptoms may be observed in the mouth of a dog with oral cancer:

  • Swollen gums
  • Bleeding from any part of the mouth
  • Visible lesions (often white)
  • Breaths smell worse than usual, or halitosis
  • Drooling
  • Pain when eating or chewing, or chewing on one side of the mouth
  • Swelling around the muzzle or eye area
  • Weight loss and loss of appetite

Oral cancers are often noticed when they begin to smell, or when dogs are having trouble eating. Some owners may pick up subtle changes when their dog is panting, opening their mouth or having their teeth brushed.

Treating a dog's mouth cancer

Oral tumours are difficult to remove. Often this is a specialist procedure, and requires advanced imaging with CT scans or MRI to determine the depth and spread of the tumour. Teeth and bone are commonly removed along with the mass, and sometimes this means removing a whole jaw bone. Chemotherapy and radiotherapy may be needed alongside surgical removal. Unfortunately not all tumours can be removed, and palliative care or euthanasia is the only option. As sad as this may seem, an animal in pain isn’t a happy animal - and sometimes it is the best option for our companions.

The prognosis and recovery chances depend on the type of tumour, location and whether the entire tumour can be removed. If metastases are present the chances of successful treatment and survival are reduced, and treatment may not be an option. Life expectancies vary, but are typically in months rather than years.

Regular checks of your dog’s mouth are crucial in spotting the early signs of problems - whether simple dental disease or something more worrying. Swift diagnosis and removal give your pet the best chance of survival. Time is of the essence. Your vet is on hand to help identify and treat problems as they arise, and any concerns you have should be discussed as soon as possible.

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