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Canine Oral Cancer

Malignant canine oral cancer is rather common in dogs and can be in the form of melanoma, squamous cell carcinoma, and fibrosarcoma. This page looks at the symptoms, causes, and conventional treatment of mouth cancer in dogs.

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Oral cancer in dogs is the fourth most common canine cancer and accounts for about 6% of all tumors.

Understandably, oral tumors cause a lot of discomfort to dogs due to their location. The tumors can also obstruct the oral passage making it difficult for the dog to eat and drink. Sometimes, their location also makes it difficult to treat.

There are two types of oral tumors in dogs - benign tumors and malignant tumors. Benign tumors are well defined and limited to a specific location. They do not spread and do not invade the bone or other tissues. Malignant tumors, on the other hand, are those that metastasize and invade other tissues or organs.

It is difficult to tell whether a growth in the mouth is benign or malignant. Therefore, it is important to take your dog to the vet for a proper diagnosis if you see any growths in his mouth - no matter how benign they look.

Benign Oral Tumors in Dogs

A common benign oral tumor in dogs is the epulis, which is most commonly seen in Boxers and Bulldogs. These tumors grow from the periodontal membrane in response to gum inflammation and appear as growths on a flap of tissue. There are often multiple growths.

There are numerous other benign growths as well, such as fibromas.

All these benign oral tumors usually have well defined borders. They do not invade the bone or other tissues and do not spread. Surgical removal of these benign tumors can usually fix the problem.

Canine Oral Cancer - Malignant Tumors

Malignant oral tumors usually occur in older dogs. There are three common malignant oral tumors in dogs. In order of frequency, they are malignant melanoma, squamous cell carcinoma, and fibrosarcoma.
  • Melanoma: This tumor is locally invasive, and metastasizes early in the course of the disease. Therefore, by the time it is diagnosed, it is usually too late - the tumor has already spread. Melanomas are usually found in the lower gums and often involve not only the gums, but also the jaw bones. Sometimes, they also occur in other places in the mouth, such as the tongue, lip and palate. They can be either dark or light gray and are most commonly seen in older dogs that have dark pigmented oral mucosa.
  • Squamous Cell Carcinoma: This tumor is locally aggressive but tends to metastasize late, if at all. This type of tumor will very commonly affect the underlying bone. Squamous cell carcinomas are commonly found in older dogs as an ulcerated red spot.
  • Fibrosarcoma: This tumor is also locally aggressive but does not tend to spread. It also appears as a red growth, which can be fibrous or ulcerated. Fibrosarcomas commonly occur in older male, large breed dogs.

Causes of Canine Oral Cancer

The exact cause of mouth cancer in dogs is not clear. However, it is believed that environmental carcinogens (cancer-causing agents) may play a role in causing oral cancer in dogs. As dogs use their nose often to smell and sniff, it is possible that carcinogens in the environment are inhaled and deposited in the dog's oral cavity where they trigger abnormal cell growths which result in cancerous tumors.

In addition, it has been reported that dogs with oral papillomas (warts caused by a virus called Papillomavirus) are at higher risk of developing malignant tumors.

Symptoms of Canine Oral Cancer

Unfortunately, symptoms of canine oral cancer are very similar to those of periodontal problems, making it difficult to diagnose. Very often, the cancer is not diagnosed until it is in an advanced stage.

Common signs of oral cancer in dogs include:
  • Excessive drooling
  • Bloody saliva
  • Bad breath
  • Difficulty chewing
  • Difficulty swallowing
  • Appetite loss
  • Weight loss
  • Facial swelling
A dog may show signs of breathing difficulty if there is a mouth tumor at the base of the tongue.

Diagnosis and Treatment of Canine Oral Cancer

A definitive diagnosis can be made by biopsy of the tumor.

In addition, chest x-rays and x-rays of the local and surrounding area of the tumor will be taken to determine if the cancer has spread, and if so, to what extent. As mentioned above, melanomas tend to metastasize early and by the time the dog is diagnosed with oral cancer, it will have already metastasized to the lungs.

Moreover, if a dog has been diagnosed with oral cancer, the vet will most likely examine the regional lymph nodes as well. Fine-needle aspiration may be necessary to biopsy suspicious nodes to check for the presence of cancerous cells.

Depending on the size, location, and type of the tumor, treatment can be one or a combination of the following:
  • Surgery
  • Radiation
  • Chemotherapy
  • Cryosurgery (freezing of the tumor)
For invasive tumors such as melanomas, aggressive surgery removing not only the tumor but also at least 2 cm of normal tissue at all margins of the tumor is necessary. Surgery may involve removing part of the upper or lower jaw. (See also our page on canine melanoma.)

For cases where clean margins cannot be achieved, or for tumors that are simply inoperable due to wide-spread invasion, the vet will likely suggest radiation therapy for palliative control.

Chemotherapy can be used as a follow-up treatment for cancers that have spread far from the primary site.

Small tumors may also be treated by cryosurgery, a procedure that uses extremely cold liquid nitrogen to freeze and kill the cancerous cells. It is also used for treating residues left behind after surgery.

As mentioned above, many cases of canine oral cancer are not diagnosed until they are in too advanced a stage for treatment. The prognosis is best for squamous cell carcinomas if they are located in the front - 50% of treated dogs survive a year or longer.

Prevention of Canine Oral Cancer

While it is impossible to totally prevent any type of cancer from occurring to your dogs, there are things that can be done to minimize the risk. For example, as mentioned above, dogs with oral papillomas are at higher risk of developing malignant mouth tumors, and papillomas usually occur to dogs with weakened immune systems, such as those who are undergoing corticosteroid therapy. It follows that strengthening the dogs' immune systems is one way to lessen the chance of contracting papillomas and oral tumors.

In addition, if at all possible, avoid exposing your dog to environmental carcinogens, such as cigarette smoke, harmful chemicals, car exhaust, etc.
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