Oral Tumors in Dogs - Melanomas

By Ryan Llera, BSc, DVM; Jan Bellows, DVM, Dipl. AVDC, ABVP; Christopher Pinard, DVM

What is an oral melanoma?

An oral melanoma is an abnormal proliferation and replication of the cells called melanocytes). Melanocytes are cells in the skin that produce pigment, typically black in color. Amelanotic melanoma is a type of tumor arising from melanocytes, but these do not produce pigment. Melanomas are the most common oral tumor in dogs and are very aggressive in that they have the highest potential to metastasize (spread).

What causes this type of cancer?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. Several breeds seem to be more predisposed to these types of tumors including Chow Chows, Cocker Spaniels, Dachshunds, Golden Retrievers, Gordon Setters, and Miniature Poodles.

What are the clinical signs of melanoma?

Lesions may appear as thickened and pigmented nodules, arising from any location within the mouth. These tumors may look small from the outside but extend deeper into the tissues than expected, invading the underlying bone. Alternately, the bone may be affected first causing significant oral swelling.

Oral pain is usually apparent, especially in dogs with tumors that have penetrated the underlying bone. Signs may include bad breath (halitosis), drooling, panting, movement or loss of teeth, bleeding from the teeth, lack of appetite or difficulty eating, reluctance to be touched on the head, facial swelling, and swelling of the lymph nodes.

How is this cancer diagnosed?

An accurate diagnosis of oral tumors requires microscopic examination of tumor tissue. Fine needle aspiration (FNA) may be pursued in cases of oral tumors. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope. In some cases, results from FNA may not be entirely clear and biopsy may be necessary.

A biopsy is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined under the microscope. This is called histopathology. Histopathology is not only helpful in making a diagnosis but can indicate how the tumor is likely to behave (probability of local recurrence or spread to other areas). In many cases with these oral tumors, biopsy is the preferred method for diagnosis.

How does this cancer typically progress?

Oral melanomas are locally aggressive, meaning they will invade the closely associated tissues and structures (tooth roots, bone, and other soft tissues. They also tend to metastasize (spread elsewhere in the body) most often to the lungs and lymph nodes.

Staging (searching for potential spread to other locations in the body) is highly recommended. This may include a blood cell count, chemistry profile to assess organ function, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. If local lymph nodes are enlarged or feel abnormal, further sampling by FNA may be pursued to determine if spread has occurred.

What are the treatments for this type of tumor?

Surgical removal is the standard treatment for all melanomas. CT scans of the head or neck are usually performed prior to surgery to determine the extent of disease, as well as for surgical planning. If local lymph nodes (submandibular lymph nodes) are affected, they will typically be removed at the same time as tumor removal. Your veterinarian may recommend removal of these lymph nodes as a preventive measure to ensure there is no spread.

If the tumor has invaded bone, its removal may be difficult, and it may be necessary to remove a portion of your dog’s jaw (upper or lower). Although this type of surgery sounds daunting, many of these tumors are painful and surgical removal provides relief.

"Radiation therapy may be pursued as a primary treatment, as melanomas respond well to radiation."

After surgery, the tissues are sent for histopathology to predict, as best as possible, the probability of local recurrence or metastasis (spread to other areas). If the entire tumor is submitted, the pathologist may be able to assess if the tumor was completely removed or if additional therapies (a second surgery, radiation, or chemotherapy) are necessary.>

In some cases, surgery may not be possible. Radiation therapy may be pursued as a primary treatment, as melanomas respond well to radiation. Radiation may be useful prior to a surgery to help shrink the tumor.

Immunotherapy, or more simply a melanoma vaccine (ONCEPT), has become available in recent years and has been shown to help improve survival times. It is meant to help treat microscopic disease after surgery has removed the bulk of the disease.  Unlike other vaccines, it does not prevent melanomas from developing.

Is there anything else I should know?

Catching this type of tumor early is always beneficial from both a management and treatment standpoint. If any abnormality is observed in your dog’s mouth, you should talk with your veterinarian to determine an appropriate course of action.

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