What Causes Oral Cancer in Dogs?

A dog’s increased predisposition to developing oral tumors has not been fully identified. Most cases seem to be a result of a combination of risk factors that will include genetic, hereditary, and environmental factors.

Cases of oral cancer in dogs appear to be higher among male dogs compared to females. Although the condition can affect any breed of dog, some breeds seem to be more predisposed to the condition, including:

• Boxer
• Chow Chow
• German Shepherd
• Miniature Poodle
• German Shorthaired Pointer
• Weimaraner
• Golden Retriever
• Gordon Setter
• Cocker Spaniel
• Scottish Terrier
• Standard Poodle
• Dachshund

Symptoms of Oral Tumors in Dogs

The symptoms of oral cancer in dogs depend on the type of tumor, its size, and rate of metastasis (spread). The tumors can be found anywhere in the mouth, including the gums, tongue, hard or soft palate, tonsils, and lips.

Affected dogs suffer from pain, especially if the tumors reach the underlying bone. Other symptoms include:

• Bad breath (halitosis)
• Drooling
• Panting
• Lack or loss of appetite
• Tooth loss or tooth movement
• Difficulty eating and drinking
• Chewing food on only one side of the mouth
• Facial swelling
• Swelling of adjacent lymph nodes
• Don’t want to be touched on the head
• Blood may be present in the dog’s food, water bowl, or bedding

What types of cancer can a dog have in their mouth?

The most common types of oral cancer in dogs are:

• Melanoma
• Squamous cell carcinoma
• Oral fibrosarcoma

1. Oral Melanoma in Dogs

Melanoma is a tumor of melanocytes, which are pigment-producing cells of the body. Oral melanoma has been considered an extremely malignant tumor with a high degree of local invasiveness and high metastatic ability. Median survival times for dogs with oral melanoma treated with surgery are approximately 17 to 18, 5 to 6, and 3 months with stage I, II, and III diseases, respectively.

The tumors can be pigmented (darkly colored) or non-pigmented (pink like gum tissue). They may appear nodular or cauliflower-like. These tumors are often seen as swellings on the gums around the dog’s teeth or on the soft or hard palate. Melanomas often form ulcers that bleed. Secondary bacterial infection is a common complication. This type of tumor may appear small but they usually extend deeper in the oral tissues and invade the surrounding bone.

2. Oral Squamous Cell Carcinomas in Dogs

An oral squamous cell carcinoma (SCC) is a malignant tumor affecting the cells that line the throat and mouth, including the tonsils and gum line. It’s the most commonly reported mouth tumor in cats, and the second most common in dogs. Oral SCC in both cats and dogs is locally aggressive, which means it will invade tissues close to the tumor.

Bowen’s disease or Bowenoid carcinoma (multicentric carcinoma) is a type of SCC in which the tumors are confined to the surface of the skin and mouth. This type, however, is rare in cats and dogs.

The cause of oral SCC has not been identified or fully established. But most experts believe it’s a complex combination of several factors - genetic, environmental, and hereditary.

The tumors appear nodular or cauliflower-like and may be pink or discolored. Some tumors break open and bleed. Although they may appear small, these tumors usually extend deeper into the mouth tissues and may invade the underlying bone.

The symptoms exhibited by the dog will depend on the tumor’s location, type, size, and degree of metastasis. Affected dogs may suffer from oral pain which can lead to excessive salivation (drooling), excessive panting, lack of appetite, bad breath, and difficulty eating. Problems with breathing and swallowing may occur when there is swelling in one or both tonsils.

The treatment for oral SCC involves surgical removal, and the prognosis is usually good. Radiation therapy may be recommended after surgery. However, there are some cases in which surgery is not possible. In these cases, radiation or other treatment protocols may be pursued. Chemotherapy is usually recommended when there is evidence of metastasis.

3. Oral Fibrosarcoma in Dogs

Oral fibrosarcomas originate from the fibrous connective tissues of the mouth. These are malignant, rapidly-growing tumors. Recurrence is very high after surgery, and metastasis is very common.

The tumors may appear as swollen areas within the mouth. They frequently ulcerate and become infected.

Surgery to remove the tumor is the standard treatment of choice for fibrosarcomas. If adjacent lymph nodes are affected, they are also removed during surgery

Treatment and Prognosis for Dogs with Mouth Cancer

Treatment of melanoma is two-pronged - localized treatment of the tumor and systemic treatment because of the high potential for metastasis.

Local control involves surgery to remove the entire tumor. To remove all of the mass, a portion of the bone of the upper or lower jaw may need to be removed. Most dogs do well after surgery without any impact on their quality of life.

Radiation Therapy

When surgery is unable to completely remove the oral tumor, radiation therapy is given to help kill any residual disease and decrease or slow down the risk for recurrence. About 75% of patients that undergo radiation therapy experienced a decrease in tumor size depending on the stage of the disease.

Canine Melanoma Vaccine

There is a vaccine that is administered once every two weeks for four treatments for dogs with melanoma. A booster vaccine is given once every 6 months after the initial 4 doses. However, the vaccine has its downsides - it can take the dog’s immune system a minimum of 2-3 months before it can mount an adequate immune response that will destroy the melanoma cells.

Chemotherapy

Chemotherapy is not recommended because it lacks efficacy. Less than 30% of patients have been shown to respond positively to chemotherapy which is often used for patients with fast-growing or aggressive tumors to slow down the growth and spread and to give time for the vaccine to work.

Read more:

Warning Signs of Cancer in Dogs

Dental and Oral Anatomy in Dogs

How to Examine Your Pet at Home: A Step-By-Step Guide

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