Melanoma in Dogs

Melanoma in Dogs: a Tumor of the Cells That Control Pigment

Melanoma is a tumor of the melanocytes or pigmented cells of the skin or mucous membranes. These cells can be found anywhere skin or mucous membranes are, so there are several types of melanoma.

Location Matters in Canine Melanoma

Melanomas tend to grow quickly and spread or metastasize, to other locations in the body. The location of a canine melanoma tumor tends to impact how aggressive it will be.¹

For example, a general rule in melanoma is that if a tumor grows on or within one centimeter of a mucous membrane, it will behave dangerously.² (The lining of the mouth and nose are examples of mucous membranes.)

Let’s discuss the main locations and types of melanoma in dogs.

Oral Melanoma (Melanoma in a Dog’s Mouth)

Melanomas that grow in the mouth are the most common and most aggressive variant of melanoma in dogs.

Oral melanomas account for 80% of melanomas,⁴ and they are also the most frequently diagnosed malignant tumor in dogs.⁶

Oral melanomas are significant enough to warrant their own article here on DogCancer.com.

Nail Bed Melanoma in Dogs

The base of the nail is the second most common location for malignant melanomas in dogs.

Nail bed melanoma accounts for approximately 15-20% of melanoma cases⁴ and about 12% of all tumors located on the toes.¹⁰ Forelimbs may be slightly more likely to be affected than hind limbs.

Nail bed melanomas can be very painful because they destroy the underlying bone.² Often these tumors look like a nail infection. They may even respond to treatments given for infection (usually antibiotics and anti-inflammatories), at first.²

Nail bed melanomas tend to metastasize at rates upwards of 50%.¹⁰ Amputation of the toe is technically curative if the tumor cells have not spread. However, an estimated 30% to 40% have already metastasized by the time they are diagnosed.²

The median survival time for nail bed melanoma is one year.²

Canine Melanoma in Mucocutaneous Junctions

Mucocutaneous junctions are where the mucous membrane meets skin. This includes tumors that grow on the vulva, anal area, and lips (although these possibly count as “oral”).

These tumors are less common but also very aggressive. One study found that although anal sac melanomas are uncommon, they have a short survival time with only 1 of 11 dogs alive after a year of treatment.⁷

Ocular or Dog Eye Melanoma

Nearly any part of the eye can grow a melanoma, but the iris or epibulbar (on the surface of the eyeball) regions are the most common.

Iris Dog Eye Melanoma

Iris melanoma occurs in the colored part of the eye. These tumors can be hard to see until they are really big.² They are benign in 80% of dogs, but even benign melanomas can be problematic, because they grow quite large and cause pain, inflammation, glaucoma (increased pressure in the eye), and vision problems. (It is interesting to note that eye melanoma in cats is more malignant, with 60% to 70% of iris melanomas being malignant.)²

Enucleation, or surgical removal of the entire eye, is usually recommended for both malignant and benign iris melanomas, though smaller benign tumors may respond to laser therapy.²

Epibulbar Dog Eye Melanoma

Epibulbar melanoma occurs on the outer eye portion, where the white sclera meets the clear cornea. Melanomas in these locations are much less aggressive.

Smaller tumors may not need treatment, though larger tumors should be removed by surgery, laser, or cryosurgery.² They are not expected to metastasize.³

Dermal, Cutaneous, or Skin Melanoma in Dogs

These melanoma tumors grow on skin with hair. Unlike in people, in dog melanomas on the skin tend to be benign.

These benign tumors are sometimes called melanocytomas.³ Dermal melanomas make up approximately 5% to 7% of all skin tumors¹⁵ and are more common in dark-haired dogs. They often look like either solitary, dark masses or are flat and wrinkly, but can also lack pigmentation altogether.¹⁵

As already mentioned, dermal melanomas are rarely malignant, but when they are, they are really aggressive.

• Skin melanomas are especially suspicious if located within a centimeter of a mucous membrane.⁵
• Approximately 12% of dermal melanomas are malignant⁶, so it is important to biopsy them or surgically remove them and send to the lab for identification.
• Alternatively, your veterinarian can try to get a cytology using fine needle aspirate, but dermal melanomas don’t usually exfoliate (let go of their cells) very well.

If your dog’s dermal melanoma does prove to be malignant, it is treated like the other types of malignant melanoma.

Non-malignant Melanomas, AKA Melanocytomas

Although benign melanomas (technically called melanocytomas) are much less common than malignant melanomas, they do exist.

Melanocytomas often grow in haired areas and arise from the external root of a hair follicle. They are more common on the eyelid.⁵ Melanocytic nevus are also very similar and appear as small, round, firm, dark masses (like a mole).⁵

As these tumors are benign and not likely to spread or cause harm over time, they are usually not treated unless they are in a position that causes discomfort or mobility problems. Your veterinarian may want to keep monitoring them over time.

Stats and Facts About Canine Melanoma

• Melanoma accounts for approximately 7% of all malignant tumors in dogs.⁹
• 80% of melanoma cases occur in the mouth.⁴
• 15-20% of melanoma cases occur in the nail bed.⁴
• Melanoma in the eye is usually benign.²

In some ways, melanoma in dogs is similar to melanoma in humans, so research and treatments for one species will help the other.⁸

One notable difference is that in humans, malignant melanoma is associated with sun damage and sun exposure, but the same association is not proven in dogs.²

What Causes Malignant Melanoma in Dogs

The exact cause of melanoma is not known. As with many cancers, it is likely caused by a combination of genetic and environmental factors.⁴

Risk Factors for Dog Melanoma

Much is unknown about what causes melanoma in dogs, or what risk factors may be associated with it. The following are possible risk factors, but with no strong data to support:

• Excessive licking one place on the skin, causing mutation in the cells.⁴
• Chemicals in the environment, hormones, or viruses.⁵
• Other sources of chronic inflammation, such as deep infections or burns.⁶

In general, neither sex is more likely to have melanoma.

It is possible for any breed of dog to get melanoma, but some breeds are overrepresented. Breeds that are diagnosed with melanoma more commonly include:^1,4,5

• Airedale Terriers
• Bull Terriers
• Chesapeake Bay Retrievers
• Chihuahuas
• Chow Chows
• Cocker Spaniels
• Doberman Pinschers
• Golden Retrievers
• Irish Setters
• Poodles
• Schnauzers

Dark-haired dogs are more likely to have dermal or nail bed melanoma.²

One study suggested that Vizslas between 5 and 11 years old are more prone to benign melanocytomas⁵, which is hopeful news for Vizsla owners.

Another study suggested that ocular (eye) melanoma, which is also usually benign, is possibly more common in female German Shepherds between 5 and 6 years old.⁵

Symptoms of Dog Melanoma

If you see any abnormal bumps or sores on your dog, or he is acting ill, schedule an examination with your veterinarian. That said, the symptoms of melanoma depend on where the tumor is located, if the cancer has spread, and how severe it is. ⁴

Oral Melanoma Symptoms

Symptoms of oral melanoma often look similar to a variety of dental issues:⁴

• Bad breath
• Abnormal chewing habits
• Refusing to eat
• Drooling
• Presence of an obvious mass on the mucous membrane

Skin Melanoma Symptoms

Dermal melanoma symptoms include:^1,4

• A visible tumor which can vary in appearance, but dark raised or flat skin patches are common
• Bleeding or ulcerated mass
• Occasionally, the melanoma will lack pigment (called amelanotic melanoma) and is pink in color. The fact that melanoma is amelanotic does not change anything about the treatment or prognosis recommendations.

Nail Bed Melanoma Symptoms

Aggressive nail bed melanomas are uncomfortable and can show a variety of signs:⁵

• Limping
• Licking toes
• Swollen toes
• Discolored nails
• Loose nails

Eye Melanoma Symptoms

Ocular melanoma is usually noticed as a dark mass in the eye or on the eyelid, a dark spot on the iris, swelling in or near the eye, or the eye is red or cloudy.⁵

Symptoms that Canine Melanoma Has Spread

If the melanoma has spread, symptoms of metastasis you might see in your dog include:⁴

• Losing weight
• Coughing
• Difficulty breathing

Getting a Diagnosis of Canine Melanoma

Diagnosis of melanoma starts with a physical exam by a veterinarian.⁴ The veterinarian is looking for just about anything abnormal on the skin and mucous membranes: dark patches, dark lumps, bleeding spots, small blisters, spots that won’t heal, or sometimes a rash on the belly, feet, or face.⁵

Fine Needle Aspirate: Possible Diagnostic Tool for Canine Melanoma

If your veterinarian finds something, or if you point out a problem area, your veterinarian will likely get a sample of the mass, called a fine needle aspirate. This is when the veterinarian uses a needle and syringe to get a few cells out of the mass, then smears it across a slide for examination under a microscope (also known as cytology). Your veterinarian may recommend sending out the slide for a pathologist to review it and use special stains that can make cells easier to identify.

Some lumps and bumps aren’t likely to aspirate well, because they are too hard or solid to get a good sample. Your veterinarian may want to skip the fine needle aspirate in these cases.

Biopsy: a More Likely Diagnostic Tool for Canine Melanoma

If your vet does take a sample and there is a complication, or they discover it is “non-diagnostic,” meaning they didn’t get a good sample, they will likely recommend skipping straight to biopsy: removing the mass surgically and sending it to the laboratory for identification.

What the Vets are Looking for That Indicates Melanoma

Several things on the cytology or biopsy can help a veterinarian or pathologist diagnose melanomas and predict how aggressively they may behave.

Ki-67

Several studies have found Ki-67 to be the most reliable indicator of how aggressive a dog’s melanoma will be.¹⁶

Ki-67 is a type of nuclear protein associated with rapid tumor growth and tumor cell proliferation. Knowing if these proteins are present may help predict aggressive behavior.⁵ The pathologist can see these proteins with the help of a special stain.

A Ki-67 index greater than 15% suggests a bad prognosis.¹⁶

Nuclear Atypia

This is when the nuclei of the cells have an abnormal appearance, and it is associated with malignancy.¹⁶ Sometimes it is reported as “mild,” “moderate,” or “severe.”

Mitototic Index

Many studies suggest this is the most accurate way to predict aggressive behavior in a tumor. The pathologist looks for cells that are right in the middle of dividing, then counts how many there are in a high-powered microscopic field.² The sample is then given a score.

In general, a tumor with less than three mitotic figures in a high-power field will likely express benign behavior and be less aggressive.²

Additional Tests for Melanoma in Dogs

There might be other tests the veterinarian may want to run when chasing down a diagnosis. For example, because surgery is the first treatment in melanoma in dogs, your dog’s general health will need to be understood before he or she has anesthesia.

In general, your veterinarian may recommend blood tests, urinalysis, or imaging procedures like X-rays, ultrasound, MRI, or CT.

If the melanoma is on the toe, they may recommend X-rays of that paw, and if the melanoma is in the eye, they may recommend more specific eye tests (such as tonometry to check eye pressure, Shirmer tear test, or a slit lamp exam).

Staging and Prognosis for Melanoma in Dogs

Staging means determining how much cancer is in the body and where it is located. We want to know how big the tumor is and if it has spread (usually to lymph nodes or lungs). The tests listed above help your veterinarian to figure out what you and your dog are facing.

Large Melanomas in Dogs Might Not Need Many Staging Tests

If the melanoma tumor is already very large, it has also likely already spread. Larger melanoma tumors are also more likely to be aggressive and are harder to surgically remove.¹

In these cases, and especially if finances are an issue, staging may not be the place to spend money. Since the prognosis is almost certainly bad in that case, seeking palliative (trying to help, not cure) and supportive care is a reasonable option.

Small and Medium Canine Melanoma Tumors May Benefit from More Staging

For small or medium tumors, prognosis is highly variable, so finding out more information up front will help you and your veterinarian make decisions.

It’s recommended to do at least basic cytology (to evaluate how aggressive the tumor is) and basic imaging (to determine if it has spread).

If the tumor has already spread to the lungs and/or lymph nodes, or it is aggressive, it carries a worse prognosis. Knowing this up front really helps with treatment decisions.

Staging Melanoma

Staging is straightforward for oral melanoma (see separate article), but it can be less clear in other melanoma sites. In general, for canine melanoma:

• Stage 1. The tumor is less than 1 centimeter in size, and has not spread. With surgery alone, median survival time is 15 to 18 months.¹
• Stage 2. The tumor is 2 to 4 centimeters in size. With surgery alone, median survival time is 6 months.¹
• Stage 3. The tumor is over 4 centimeters in size or has spread to lymph nodes. With surgery alone, median survival time is 3 to 4 months.¹
• Stage 4. The tumor has spread to the lungs. Surgery is usually not even attempted in these cases unless partial removal will help with palliative care to improve the dog’s quality of life. Median survival time is 1 to 2 months,¹ but may be only a couple weeks.

Once you have a diagnosis and know the approximate stage and prognosis for your dog’s melanoma, your veterinarian can guide you through the different treatment options.

Treatment for Canine Melanoma

Cancer treatment in dogs, in general, is not usually about getting a “cure.” Instead, the focus is on improving and maintaining the quality of life while also hopefully extending the dog’s life beyond what would happen if the cancer wasn’t treated.

The goals of treatment for malignant melanoma in dogs specifically are:

• To control the local tumor.
• To stop it from spreading.
• To control any spread that has already occurred.

Traditionally, this has meant surgery and radiation, which are still the mainstays of treatment for melanoma in dogs.

However, a newer and very effective vaccine option can be used alone or be added to traditional treatment.

In general, chemotherapy has not been effective, but some new studies show promising results.²

Recurrence of melanoma is common, so multiple rounds of treatments are often required.⁵

Let’s look at each of these treatments in a little more detail.

Surgery for Canine Melanoma

Surgery is nearly always recommended to remove the primary tumor, no matter where it is located in the body.² The median survival time for surgery alone is approximately 9 months, but this is highly dependent on tumor location, size, and if it has spread.⁵

• If the surgeon gets clean margins, meaning the surgeon got all the tumor, then possibly only the vaccine is recommended after that.²
• If the surgeon did not get clean margins, and some cancer cells were left, radiation and the vaccine are usually recommended.²
• For nail bed melanoma, the entire toe is usually amputated, as the tumor has often spread to nearby bone. Most dogs have no trouble adjusting to a missing toe, especially one that has been causing pain and lameness.

Surgical removal of lymph nodes is also often recommended if the melanoma has spread already. By the time it is diagnosed, 30% to 40% of melanomas have already spread.⁵

Chemotherapy for Dog Melanoma

The use of chemotherapy to treat melanoma is highly variable. It does not work very well in human melanoma treatment, but some veterinary oncologists will add chemotherapy to other treatments if the tumor has already spread.²

One of the more common chemotherapy protocols is a dose of carboplatin every three weeks, for a total of 4 to 6 doses.⁴

Some recent studies are once again looking at some chemotherapy protocols that could be beneficial in melanoma treatment. One study showed that carboplatin and piroxicam, given to Stage 4 patients extended median survival time from 30 to 119 days.²

So far one case study has found that Palladia (a chemotherapy commonly used to treat mast cell tumors) may also be effective for melanoma.¹⁷ This requires further investigation to be sure if this will be a reliable treatment option.

Radiation for Melanoma in Dogs

Melanomas are relatively sensitive to radiation, so using this method can reduce recurrence or regrowth of the tumor. Radiation is often started about two weeks after surgery to remove the primary tumor. It treats areas where the surgical margins were not clean and cancer cells were left behind⁴.

Large doses of radiation at less frequent intervals tend to work best,⁵ which allows the surrounding tissue to heal in between treatments.

• A typical radiation protocol is one treatment per week for 3 to 6 weeks.⁵
• Palliative radiation protocols that are just intended to help the dog feel better may be less frequent or have varying doses.

Radiation is also very helpful to treat locations where surgery is not possible, such as in bones, teeth, jaws, tongues, and lymph nodes.⁵ If only radiation is used, the median survival time is 9 months(5), but varies depending on tumor size, location, et cetera. One study with a rare nasal melanoma (in which surgery was not an option) reported a median survival time of several months with radiation alone, which was a good outcome under the circumstances.¹²

The side effects of radiation are usually mild and self-limiting, and only affect the area that was irradiated. Symptoms include hair loss, changes in skin color, skin dryness, and irritation.⁹

Immunotherapy for Melanoma in Dogs: the Dog Melanoma Vaccine

For about the last decade, we have had access to a melanoma vaccine called Oncept^® manufactured by Merial.¹³

Traditional vaccines are designed to train the body to recognize a disease before it happens, but immunotherapy vaccines are a little different. The Oncept vaccine is used as a treatment after melanoma has been diagnosed.⁴ It is not used to prevent melanoma.

The Oncept melanoma vaccine for dogs works by alerting the dog’s immune system to the problematic melanoma cells. Melanoma tumor cells have a protein called tyrosinase, which helps it make melanin.¹³ The vaccine “alerts” the dog’s immune system to this protein, inciting the dog’s own immune system to attack the melanoma tumor cells.

Oncept is usually given as one injection every two weeks for a total of four doses. Then a booster is usually given every six months.1It is generally available through veterinary oncologists.

The vaccine works best in the following situations:^2,13

• Oral or nail bed melanoma
• Stage 2 or 3 melanoma that has not yet spread to local lymph nodes
• Stage 2 or 3 melanoma where the local lymph node has been removed

This vaccine appears to be very effective and offers a lot of hope to dogs with melanoma.

• Many dogs survive over a year with the vaccine.²
• A recent study showed that 75% of dogs in Stage 2 or 3 who had the primary tumor surgically removed and then received the vaccine lived over 15 months.¹ Without the vaccine, mean survival time was 3 to 6 months.

The melanoma vaccine is well tolerated, with minimal side effects.⁴ Some dogs will get a mild fever or pain at the site of the injection¹³.

The cost of the Oncept vaccine is about $1,000 to $1,500 per dose, but this will vary depending on where you live.⁴

Diet for Dogs with Melanoma

The most important thing when feeding a dog with melanoma is to ensure that her diet is complete and balanced, providing all the nutrients her body requires. There are no specific dietary recommendations aimed at dogs with melanoma, though dogs with oral melanoma may need a soft or canned diet to make eating less painful.

Supplements for Melanoma in Dogs

There are no specific supplements targeting canine melanoma patients, but supplements used in cancer and for general immune support may be beneficial.

Integrative Therapies for Melanoma

There are many novel treatments being studied to treat malignant melanoma. Immunotherapy treatments in particular seem to hold some promise due to melanoma’s close association with the immune system.⁶

In Brazil and Argentina they are working on electrochemotherapy studies, which seem both fascinating and promising. With this technique, researchers inject a chemical into the tumor, then electrocute it lightly.⁹

While not specific to treating melanoma, massage, acupuncture, and touch therapies may be useful to help control pain and maintain quality of life.

Follow-Up After Treatment for Canine Melanoma

No matter how you decide to address your dog’s melanoma, you will need to follow up with your veterinarian and oncologist.

For tumors that appear to be well-controlled by treatment and have not spread, oncologists typically recommend scheduling rechecks every three months.¹ At these visits you should expect at least a physical exam to check the previous tumor site and lymph nodes, and chest X-rays to check for spread. If your dog is getting Oncept, the vaccine needs a booster every 6 months.

Palliative Therapy for Dogs with Melanoma

Palliative therapy is commonly recommended for dogs with advanced melanoma cancer, and melanoma that has metastasized. It may also be recommended if your dog has other life-limiting conditions that make cancer treatments more difficult or impossible.¹¹

With palliative therapy, the priorities switch from treating cancer to increasing life quality. You and your veterinarian will keep your dog comfortable and aim to maintain and increase his or her quality of life.

You will work with your veterinarian to determine the best follow-up schedule to ensure that your dog is comfortable and living the best life that she can even with this diagnosis.

What the End Stages of Melanoma in Dogs Look Like

Melanoma is aggressive and metastasizes quickly, and so death is often by euthanasia. A peaceful, pain-free, and fear-free death is the best option in the following scenarios:

• When your dog can no longer eat comfortably (usually this is oral melanoma).
• When the tumor has spread to the lungs and your dog cannot breathe.
• When the tumor spreads to internal organs and affects the function of the gastrointestinal tract, it causes him to lose weight or refuse to eat.
• When your dog is feeling pain from primary or metastatic tumors.

If you start to wonder if it is time for hospice or to say goodbye, or you need help knowing when to schedule the day for humane euthanasia, speak to your veterinarian to get a compassionate and realistic understanding of your dog’s overall health and likely course of symptoms.

Prevention Strategies for Melanoma in Dogs

Because we don’t have a specific cause, there is no known prevention for melanoma in dogs.⁴ As with all cancer prevention, it is recommended to keep your dog healthy in general with a healthy diet, regular exercise, and regular veterinary checkups. Your dog should have an exam by your veterinarian at least once a year.

Early detection of melanoma brings the best prognosis. Pay attention to your dog’s skin, and have any masses or lesions checked out right away. A monthly nose-to-tail home exam will help you with this.

If you have a young dog, consider getting them pet health insurance. Pet insurance won’t prevent melanoma, but if your dog is unlucky enough to get cancer, the insurance policy will help you get him the treatment he needs.