10 Dec Oral Maligant Melanoma in Dogs
Oral cancer accounts for 6 percent of all tumors in dogs. Approximately 45 percent of oral tumors diagnosed in dogs are malignant. Oral masses should always be evaluated by a veterinary dentist due to the high rate of malignancy. These kinds of tumors, including oral malignant melanoma in dogs, are aggressive, grow quickly, and often metastasize (spread) to other parts of the body.
What are the symptoms of oral malignant melanoma?
Malignant melanoma is the most common oral malignant tumor seen in dogs. Clinical signs of oral cancer may include facial swelling, oral bleeding, mobile teeth, weight loss, and oral pain. However, it is important to remember that all of these clinical signs can occur with severe periodontal disease. Routine oral care is vital to ensure the mouth remains healthy and allows for early detection of potentially cancerous growths.
Dogs of all ages may be affected, but the risk increases with age. It often presents as a darkly pigmented, ulcerated mass affecting the lip, gingiva, oral mucosa, or tongue. Breeds with pigmented mucosa may be at increased risk. It may also be non-pigmented (amelanotic).
How are oral tumors diagnosed?
Melanoma of the oral cavity is very aggressive and commonly metastasizes to the lungs. Diagnosis is achieved through a combination of an anesthetized oral exam, dental imaging, and biopsy. Advanced dental imaging such as cone-beam CT or conventional CT is strongly encouraged and warranted for appropriate surgical planning. Additionally, it is recommended that biopsy samples are submitted to a histopathologist that specializes in oral diseases.
What are the stages of oral malignant melanoma in dogs?
Once a diagnosis has been obtained, staging is recommended to determine the prognosis. The size of the tumor is important when considering prognosis. The World Health Organization has a staging system that aids in prognosis.
Stage I disease is a tumor less than 2 cm in diameter. Stage II disease is a tumor 2–4 cm in diameter. Stage III disease consists of tumors 4 cm or larger. Stage III also includes tumors of any size with local lymph node involvement. Stage IV disease includes any tumor with evidence of distant spread, such as in the lungs. The average survival periods have been reported as follows with surgery:
- Stage I: approximately 17-18 months
- Stage II: approximately 6 months
- Stage III: approximately 3 months
- Stage IV: approximately 1 month (surgery not indicated)
How is the disease treated?
Surgical excision with radiation therapy is the treatment of choice. In a study that evaluated the outcome of dogs with curative intent surgery, 45.7 percent of dogs had disease progression with a progression-free interval of 508 days. This means that nearly half the dogs that underwent surgery with the goal of having surgical margins free of cancer cells had the disease recur about 1.5 years later.
Additional treatment options include radiation therapy and chemotherapy. Unfortunately, melanoma is resistant to chemotherapy. Immunotherapy, in the form of ONCEPT, a canine melanoma vaccine, has been developed. It has been shown to be most efficacious when the tumor has been locally controlled with surgery. In many cases, the patient may succumb to local tumor infiltration or metastatic disease before obtaining a therapeutic benefit.
Board-Certified Veterinary Dentist in Colorado Springs
Despite a poor long term prognosis, treatment of malignant melanoma can lead to extended survival time if diagnosed early. Proper post-operative care should be observed to help Fido recover. Daily oral home care by the owner and routine evaluations by the primary care veterinarian can help determine if oral abnormalities, such as oral malignant melanoma is present. At Animal Dental Care and Oral Surgery (serving Colorado Springs, Loveland and Castle Rock, CO) we believe that every pet is entitled to a pain-free and comfortable mouth. Please reach out to us with any oral health concerns for your pet.
1. Bergman PJ. Canine oral melanoma. Clin Tech Small Anim Pract. 2007 May;22(2):55-60.
Photo by James Barker on Unsplash (12/10/2020)