Oral Melanoma in Dogs

About Oral Melanoma

Melanoma is the most common oral tumor in dogs. Also called melanocytic tumor, it is a malignant tumor of the melanocytes (a specific type of skin cell that makes the pigment melanin).

Because melanocytes can be found in skin tissues, melanomas are also found elsewhere in and on the body, but in this article, we are focusing on the oral type.

When in the mouth, melanomas are locally invasive, which means they grow rapidly into the surrounding tissues. They are also highly metastatic, which means they go to distant sites in the body. They can spread to nearby lymph nodes, the bones of the mouth and jaw, the lungs, the liver, and the kidneys.

Oral melanomas typically first appear on the gums, lips, roof of the mouth, and/or the tongue. They may appear pigmented black or be the normal pink color of the mucosa of the mouth.

Unfortunately, oral melanomas are extremely aggressive, and most are ultimately fatal.^1,2 That said, good treatments are available, and dogs experience good quality of life during those treatments. The goal is to gain longevity and life quality, not cure, and it is worth considering all your many options.

Stats and Facts About Oral Melanoma

These are some of the important statistics to understand about oral melanoma in dogs.

• 30-40% of all oral tumors are melanomas³
• Up to 80% of dogs with oral melanomas develop metastatic disease (mostly to the lymph nodes and lungs).³ 38% of dogs with oral melanoma have metastatic lesions to the central nervous system (brain and spinal cord)⁴
• The average age at the time of diagnosis is 11.4 years⁵

What Causes Oral Melanoma?

There are no known causes specific to oral melanoma at this time, however there are theories that trauma, chemical exposure, hormones, and genetics may play a role in its development.²

Risk Factors for Oral Melanoma

Any dog can develop oral melanomas; however, some breeds are more likely:^2,3,6

• Cocker Spaniel
• German Shepherd Dog
• German Shorthaired Pointer
• Golden Retriever
• Gordon Setter
• Miniature Poodle
• Chow Chow
• Boxer

Symptoms of Oral Melanoma

Dogs are often diagnosed with oral melanoma when they get routine oral care, or during a wellness exam. Possible symptoms of oral melanoma include:⁶

• None, if they are found by a veterinarian during a wellness exam
• If the tumor is towards the front of the mouth, you might see it
• Bad breath
• Excessive drooling
• Difficulty eating or swallowing
• Pain while eating
• Reluctance to eat
• Pawing at the mouth
• Bleeding from the mouth
• Tooth loss
• Weight loss

How Oral Melanoma is Diagnosed

Many dogs are diagnosed after a teeth cleaning, because veterinarians can see the entire mouth during that procedure. They will often take a sample of a suspicious area to send out for biopsy.

A biopsy is the preferred method of diagnosis since melanomas can mimic many other tumor types, and special stains and a pathologist’s opinion is often required.

Your veterinarian may also take a small sample of the tumor via a fine needle aspirate, although this may not provide enough information for a definitive diagnosis.

It is important that any oral mass is biopsied because you cannot tell which oral masses are malignant just by looking at them.³

Prognosis and Staging for Oral Melanoma

Staging is the process of finding out where a tumor is located and the severity of the case. Because oral melanoma is both locally invasive and highly metastatic, the full workup includes many tests that look for spread. The reasoning behind this is simple: when you know if there is spread and how much spread there is, you can make confident treatment choices.

Staging for oral melanoma may involve:^1,3,6,7

• Labwork to assess general health (bloodwork and sometimes urinalysis)
• Chest X-rays or a CT scan to look for spread
• Abdominal ultrasound to look for spread
• Lymph node aspirates or biopsies to look for spread

Swollen lymph nodes are always alarming, but it does not necessarily mean that oral melanoma has spread. That is why lymph nodes should be aspirated or biopsiedto determine if the cancer has spread.7

To look for local invasion, a CT scan is also recommended to evaluate how aggressive the tumor is in the mouth and nearby areas.

Based on these test results, your veterinarian will give you the stage of your dog’s oral melanoma:1,3,6

Stage I Oral Melanoma: the primary tumor is smaller than 2cm (about 0.79 in) in diameter and has not spread.

Stage II Oral Melanoma: the primary tumor is 2-4cm (about 0.79 inch to about 1.57 inch) in diameter and has not spread.

Stage III Oral Melanoma: the primary tumor is greater than 4cm (about half the length of the long edge of a credit card) in diameter and may or may not have spread to the lymph nodes.

Stage IV Oral Melanoma: the primary tumor is any size and there is evidence of spread of the tumor to other parts of the body.

The prognosis, or best guess as to how the disease will progress and respond to treatment, depends on the size of the mass, the treatment methods given, and whether the tumor has already spread to other parts of the body.³

• Without any treatment at all, prognosis is extremely poor. Many dog lovers end up electing euthanasia for their dogs after approximately 2 months.
• The best prognosis is found if the melanoma is Stage I and surgery is performed with clean margins (survival time is approximately 17 months).¹
• With radical surgery and wide margins (see below), median survival time is 8-10 months1
• With radiation therapy alone, median survival time ranges from 5.3 to 11.9 months⁵
• Chemotherapy has not been found to significantly increase survival times⁵

Surgery, Radiation, and Chemotherapy Treatments for Oral Melanomas

As aggressive as oral melanomas are, they are also usually responsive to treatment. Dogs do better if:

• The tumor is caught early
• The tumor is smaller
• The treatment is very aggressive

What’s aggressive treatment? Surgery is considered the most important part of treatment for most dogs. Surgery followed by radiation therapy and immunotherapy (the melanoma vaccine) is typically the most aggressive and successful course of action. However, each dog and each cancer and each family is different, and choices must be made based on what is right for them.

In general, the goal of treating cancer in dogs is not usually about “curing” the cancer, but instead about improving and maintaining a good quality of life while also hopefully extending the dog’s life. This is certainly true for oral melanoma.

Surgery

The most critical part of treatment is surgical removal of the tumor. The goal is wide margins (ideally greater than 2cm, including through bones of the jaw), with the removal of any lymph nodes that contain cancerous cells.⁵ This can be a very extensive surgery and not every general practice veterinarian will feel comfortable performing it. It may require going to a specialty surgical center.

While removing the jaw seems very extreme, most owners are satisfied with the surgery. Oral tumors can really hurt, so when they are gone, dogs may feel better. Owners report that their dogs still eat well and are more comfortable after the surgery.¹²

The median survival time after surgical removal of the jaw is 8-10 months.8 If a more conservative approach to surgery is taken, there is a much greater risk of regrowth of the tumor.

Radiation

Radiation therapy can also be an important part of treatment for dogs with oral melanomas. Radiation therapy can be used alone or in conjunction with surgery and/or chemotherapy.¹²

The overall response rate is 82-94%, however these statistics include partial responses as well as complete responses. There is a local recurrence rate of 11-27% and the median survival time is 5.3-11.9 months.⁵

There are many proposed protocols for radiation therapy to treat oral melanomas. The most traditional approach recommends daily treatment for 18 weekdays, straight.

However, the 18-day protocol may lead to more acute side effects (corneal ulcers, skin irritation, irritation of the mucous membranes of the mouth, etc.), so a hypo-fractionated course is often recommended.

With hypo-fractionated radiation, fewer treatments are given but the dose per treatment is higher. This may cause fewer short term side effects, but risks more long-term side effects like bone damage, nerve damage, and others.1²

Immunotherapy Specifically for Oral Melanoma

Investigations have looked at using the body’s own immune system to find and destroy cancer.

Dogs with melanoma may benefit from treatment with Corynebacterium parvum, a type of bacteria which is used as a non-specific (meaning not specifically for aimed at oral melanoma) immunotherapy to boost the immune system for patients with cancer.¹³

Reovirus is a type of RNA virus also being studied in both human and canine oncology. It has been shown to induce cell death in many tumor types, including melanoma.¹⁴

Gene therapy is also being researched as an approach for both canine and human melanoma alongside surgery and has yielded promising results but is not widely available outside of a research setting.¹⁵

There is one other immunotherapy that is specific to dogs with oral melanoma: the melanoma vaccine called ONCEPT.

ONCEPT, “the Melanoma Vaccine”

Vaccines are typically used to prevent disease; however, a vaccine has been developed to be given as part of the treatment course for melanoma in dogs.

ONCEPT is recommended for dogs diagnosed with advanced melanoma who have already had surgery or radiation to treat the original tumor. It is used to control metastatic disease and has been shown to increase survival time.

The vaccine is made with human tyrosinase, which stimulates the dog’s immune system to attack melanoma cells (which contain a similar tyrosinase protein). This vaccine is very safe with minimal side effects. Some dogs have a mild skin reaction at the vaccination site, a little soreness, or a mild fever. It is currently only available through veterinary oncologists.^16,17,18

ONCEPT® is a needle-free, transdermal (through the skin) vaccine that is given every two weeks for four doses with a booster given every 6 months thereafter.

Chemotherapy for Oral Melanomas

Chemotherapy is not typically used as a standalone therapy, but it is recommended to be given alongside other more effective treatments such as radiation therapy and/or surgery.^6,9

While there is a lack of evidence to support chemotherapy as an effective treatment for oral melanoma, veterinary oncologists may still recommend a course depending upon the case, typically injectable carboplatin every three weeks.

Cisplatin (although IV cisplatin is rarely used in veterinary medicine) and masitinib have also been studied for efficacy against oral melanoma with only minimal response.^5,10,11

Electrochemotherapy has also been studied as a treatment method for oral melanoma, however an ideal protocol is not yet established. In electrochemotherapy, a chemotherapy drug that typically does not get into the cancer cells well is paired with electric pulses aimed directly into the tumor. This allows the chemotherapy drug, usually bleomycin or cisplatin, to enter the cancer cells. The response rate is similar to that of radiation therapy, however more research is still needed to determine the specifics of the treatment. ¹¹

Dietary Considerations

Many dogs with oral melanoma will benefit from a soft diet since oral tumors can cause discomfort while eating. There is no current “official” dog cancer diet, but there are many articles on diet on this site.

Supplements

There is no supplement that specifically targets oral melanoma, but there are many articles on supplements on our site.

Always consult your veterinarian before adding a supplement to make sure that it is a good fit for your dog and that it won’t interfere with any of her medications or treatments. Also only add one supplement at a time, so that if your dog reacts to it poorly, you will know exactly which thing she didn’t tolerate.

In most cases it is better to choose a few supplements that target your dog’s primary needs, rather than throwing a bunch of supplements at her. This will also help to keep costs down.

Integrative Therapies

One small study of 11 dogs found that Lupeol, a naturally occurring chemical in certain fruits and vegetables, decreased the rate of recurrence and increased survival time in dogs who had surgery to remove oral melanoma. No adverse reactions were found in this study.¹⁹

A case study was published in which a dog with oral melanoma was treated with Lupeol injections, hyperthermia treatments, and cultured dendritic cells and interleukin-12 injections. The dog had very good quality of life and showed no recurrence or evidence of metastasis six months after treatment. This was only one dog, but more research should be done to see if this treatment strategy could work for other dogs.²⁰

Oral Melanoma Research Trials for Dogs

We will update this article with links to clinical trials as they become available.

What the End of Life Looks Like for Dogs with Oral Melanoma

Even though there are many treatment options available, oral melanoma is often fatal. As the disease progresses, dogs may have difficulty eating as the tumor grows or refuse to eat if the tumor is causing pain. The tumors may bleed and be prone to infection, making dogs feel unwell. Dogs may have trouble breathing if the melanoma spreads to the lungs or starts to block the airways. These are all signs of diminishing quality of life and should be assessed by your dog’s veterinarian for hospice care.

Prevention Strategies

Check your dog’s mouth regularly! We know that the smaller the tumor is when it is diagnosed, the better the outcomes can be. Any mass found in your dog’s mouth should be evaluated as soon as possible so treatments can be most effective.

Daily toothbrushing and regular veterinary dental cleanings is also a good idea.

As research into a preventative vaccine for dog cancer continues in the VACCS trial, we may eventually find it helps oral melanoma.