Melanomas of a dog’s skin or paws (cutaneous melanomas) are growths that arise from pigment-producing cells and may be benign or malignant. Integrative veterinarian Dr. Julie Buzby explains the causes, locations, appearance, diagnosis, treatment, and prognosis for skin or paw melanomas in dogs so that dog parents know what to expect.
Dogs are susceptible to all sorts of benign and malignant growths as they age. One common tumor type that affects older dogs is melanoma. These growths can take many forms and develop anywhere on a dog’s body.
Those that appear in the mouth are called oral melanomas and are typically malignant and very aggressive. By contrast, ocular melanomas (limbal or uveal melanomas) are usually benign, although they can still interfere with a dog’s vision. The third primary type of melanoma is cutaneous melanoma (skin and paw melanomas), which we will discuss here.
What is a cutaneous melanoma in dogs?
“Cutaneous” is the medical term for skin. Thus, a cutaneous melanoma is a tumor that grows on the skin and originates from melanocytes (cells that produce the pigment melanin). Since paw pads and toenails are specialized skin structures, melanomas in those areas are also called cutaneous melanomas. Some skin or paw melanomas are benign, while others are malignant. Where a cutaneous melanoma grows can sometimes predict whether or not it has a high chance of being cancerous (malignant).
Malignant melanomas of the skin and paws
Melanomas that grow on the paw pads, nail beds, lips, eyelids, nostrils, and genital area have a much higher chance of being cancerous. These melanomas grow quickly and sometimes become ulcerated. If the melanoma involves the paw pad or nail, it can cause pain and limping. About 40-60% of malignant cutaneous melanomas will metastasize (spread) to lymph nodes, lungs, liver, spleen, or other organs.
Benign skin melanomas
On the other hand, 80-90% of melanomas in dogs that occur on the haired skin of the face, trunk, and legs are benign. They grow slowly and rarely spread to other areas of the body.
What causes skin and paw melanomas in dogs?
There is no one specific cause for cutaneous melanomas. But veterinarians have identified several risk factors that may increase a dog’s susceptibility to them.
Due to an inherent increase in the amount of melanin present, dogs with darker coats and darker skin pigmentation are slightly more at risk for developing melanomas than lighter-skinned dogs. Some studies also suggest that male dogs may be more at risk than females. Interestingly, UV light exposure is not considered a significant risk factor for dogs, in contrast to what is the case for melanomas in people.
As with many conditions, genetics may play a role in the development of melanoma. It is more common in certain breeds of dogs, including:
- Boston Terriers
- Boxers
- Chow Chows
- Cocker Spaniels
- Doberman Pinschers*
- Golden Retrievers
- Irish Setters
- Poodles*
- Rottweilers
- Schnauzers*
- Scottish Terriers
- Vizslas
*Interestingly, veterinary researchers estimate that almost 75% of melanomas diagnosed in Dobermans and Miniature Schnauzers are benign. And nearly 85% of melanomas in Poodles are malignant.
What do cutaneous melanomas in dogs look like?
Cutaneous melanomas can grow just about anywhere on the skin or paws and can vary in appearance.
It’s logical to think that a melanoma would always appear dark brown or black due to its melanin content. However, veterinary researchers estimate that roughly one-third of melanomas develop without pigment. Called amelanotic melanomas, these growths are often pale pink in color due to an absence of melanin granules.
Thus, melanomas on a dog’s skin may be black, brown, mottled, pink, or red in color. They vary in size and shape, with some being raised and round and others being flat or wrinkly. Many skin melanomas (benign or malignant) start out looking like moles or warts.
Characteristics of malignant melanoma on a dog’s skin
In general, melanomas thicker than one centimeter tend to be malignant, but this isn’t always the case. Additionally, malignant melanomas may become ulcerated, irritated, or start bleeding. When located on the lip, malignant melanomas are often pedunculated (on a stalk) and have a bumpy, irregular surface.
Characteristics of malignant melanomas of the toes
Digit melanomas have a high chance of being malignant and represent roughly one quarter of all toe tumor diagnoses in dogs. Tumors located on a toe can cause swelling of the digit, loss of the nail, and destruction of the bony tip of the toe. Initially, it may look like the dog has a painful nail infection that doesn’t totally resolve. However, there is actually a tumor invading the nail bed.
Additional symptoms of malignant melanoma
Other general symptoms of malignant melanoma include:
- Lameness: Melanomas of the paw pad or toe can be painful, causing limping in dogs.
- Excessive licking: Pain or secondary infection may cause the dog to lick the area frequently.
- Itching or irritation: Some melanomas are irritating to the dog. Scratching the area excessively may lead to secondary skin infections (pyoderma in dogs).
- Lethargy: Due to pain or tumor spread, your dog might withdraw from the family, be a lethargic dog, or generally feel unwell.
If you find a mass or see symptoms, make an appointment with your vet
We have discussed some general characteristics of benign or malignant melanomas. But there is no way to tell for sure if a mass is benign or malignant by looking at it with the naked eye. Only diagnostics like an aspirate or biopsy can make that determination. Thus, if your dog develops a lump on his or her skin or paw, it’s best to schedule an exam with your veterinarian promptly.
How are skin and paw melanomas diagnosed in dogs?
After examining your dog, your vet will perform several diagnostic tests. They can help accurately identify the growth, assess your dog’s overall health, and look for tumor spread. These tests include:
Fine Needle Aspirate (FNA)
Performing an FNA involves using a small needle to obtain cells from the mass and then looking at them under the microscope. The procedure isn’t difficult, but it may not always provide a diagnostic result since melanomas do not easily shed cells.
In addition to performing an FNA of the mass, the vet may use the same technique to collect samples from local lymph nodes near the growth. This helps your veterinarian determine if cancerous cells have migrated from the tumor to other areas of the body.
Biopsy and histopathology
A biopsy is the gold standard for diagnosing melanoma. The vet must collect biopsy samples while your dog is under anesthesia to avoid causing pain. Then he or she will send the samples to the diagnostic lab to be stained and viewed under the microscope.
In addition to determining the tumor type and whether it is benign or malignant, histopathology allows the veterinary pathologist to verify if the surgical margins are free of cancer cells. This is important because the treatment plan differs if cancerous cells are left behind.
Occasionally, special stains (immunohistochemistry) are necessary if the veterinary pathologist is suspicious of an amelanotic melanoma.
Imaging
X-rays, CT scans, and abdominal ultrasounds are valuable imaging tools in dogs with skin or digit melanomas. They help the vet identify metastasis or rule out other potential conditions with similar symptoms, like osteomyelitis (bone infection).
Bloodwork and urinalysis
Blood tests for dogs and a urinalysis give your vet an overview of your dog’s overall health. This is important since dogs often need to undergo anesthesia for diagnostic testing or mass removal.
What are the stages of melanoma in dogs?
Based on the information he or she gathered, the vet will assign a stage to your dog’s melanoma. Accurate staging of a melanoma helps your veterinarian or veterinary oncologist determine which treatment options will be the safest and most effective for your dog. In 2016, the World Health Organization adapted its human melanoma staging guidelines to apply to canine melanoma cases:
- Stage 1: Tumor size <2 cm with no lymph node involvement and no metastasis
- Stage 2: Tumor size 2-4 cm with no lymph node involvement and no metastasis
- Stage 3: Tumor size >4 cm with or without lymph node involvement, but no metastasis to other organs, OR any size tumor with lymph node metastasis
- Stage 4: Tumor of any size with evidence of lymph node involvement AND metastasis to other organs
What is the treatment for skin and paw melanomas in dogs?
Regardless of the location of a melanoma and whether it is suspected to be benign or malignant, surgical excision is the treatment of choice. As a general rule, the goal of surgery is to excise the entire growth with wide enough margins that no tumor cells remain in the surrounding tissue. That said, complete removal of the tumor can sometimes be challenging.
Surgical removal of melanomas on the skin
In most areas, surgical excision of the growth with wide margins is feasible. However, some dogs may need radiation therapy as an adjunct treatment if tumor cells remain at the surgical site.
Surgical removal of digit melanomas
Growths on the toe can be very aggressive and painful. Thus, surgical removal of the entire affected digit is often recommended. In some cases, taking the adjacent digit may also be necessary to ensure the margins are clean (free of cancer cells) and to effectively relieve pain.
Surgical removal of paw pad melanomas
Any surgical procedure involving a paw pad is challenging since there is very little skin to close after excision of the tumor. If the surgeon is unable to get wide, clean margins around the growth, there’s an increased risk that microscopic cancer cells could still be present after surgery.
Some dogs may even need to undergo dog leg amputation if the affected pad is a large, weight-bearing pad or there is evidence of metastasis to nearby lymph nodes.
Additional treatments for skin and paw melanomas
Based on the biopsy results and staging, the vet or veterinary oncologist may recommend additional treatments after tumor removal. These include:
Radiation
In addition to addressing residual cancer cells after mass removal, radiation therapy might be an option for tumors that aren’t amenable to surgery. However, there is a lack of data about using radiation for skin melanomas.
Chemotherapy
There are mixed opinions on the efficacy of chemotherapy in the treatment of melanoma, with response rates typically less than 30%. However, chemotherapy can serve as a rescue treatment for dogs whose tumors have recurred or for those with widespread metastasis.
Oncept® canine melanoma vaccine
While initially designed for dogs with oral melanoma, the Oncept® canine melanoma vaccine may increase survival rates in dogs with other types of melanomas. For example, a study published in the Journal of Veterinary Internal Medicine looked at using a melanoma vaccine for dogs with digit melanomas. In this study, surgical removal plus the melanoma vaccine provided improved survival times when compared to typical published survival times for surgery alone.
The veterinary oncologist will deliver the melanoma vaccine for dogs as a series of intramuscular injections. Dogs who qualify for the treatment will receive one injection every two weeks for four doses. Then they will receive booster vaccinations at six and 12 months.
Note: Unlike what you typically associate with the word “vaccine,” the dog melanoma vaccine is intended for treating, NOT preventing, melanoma.
Gilvetmab
Gilvetmab is a newer option for treating melanomas or mast cell tumors in dogs. This injectable medication works by helping the immune system kill the cancer cells. As of now, gilvetmab has conditional approval by the USDA, meaning that more studies are in progress to evaluate its safety and efficacy.
Pain medications
During their recovery, dogs need effective pain management, especially if they had a toe or leg amputation. Plus, if the mass is painful, the vet may prescribe pain medications prior to the surgery.
Non-steroidal anti-inflammatories (NSAIDs) such as carprofen for dogs, meloxicam, or grapiprant are common choices. Or, the vet may recommend gabapentin for dogs, especially if the dog has neuropathic pain (nerve pain).
Palliative care
Hospice care for dogs is available for advanced cases of melanoma or when the tumor cannot be surgically removed. The goal of palliative care is to keep your dog comfortable and preserve an acceptable quality of life for the remainder of his or her time with you. Your veterinarian or a vet who specializes in end-of-life care can work with you to develop a plan that is right for your dog and your family.
What is the prognosis for cutaneous melanoma in dogs?
The biggest determinant of prognosis for melanoma in dogs is whether the tumor is benign or malignant.
Benign melanomas will not impact the lifespan of your dog, but they can sometimes cause discomfort if they grow somewhere like the armpit. Typically, surgical removal is curative. However, it is always possible for your dog to develop new melanomas or other masses. Thus, it is important to have your vet evaluate any masses that pop up.
With malignant melanomas of the skin or paws, as with most types of cancer, the prognosis differs based on the location, size, and stage of the tumor, and the overall health of the dog. For example, dogs with a stage 1 tumor are going to have a significantly better outlook than those with a stage 3 or 4 melanoma.
NOTE: There are multiple papers in the veterinary literature examining prognostic factors and survival times. Thus, it isn’t possible to represent them all here. While the information below can give you a general idea of what to expect, the best way to find out your dog’s prognosis is to talk to your vet or veterinary oncologist. They will be able to speak to your dog’s particular situation.
Malignant paw melanomas in dogs
Malignant digit melanomas (those of the nail bed or paw pads) are aggressive and often metastasize. Veterinary clinicians estimate that 30% of dogs may already have metastatic tumor growth at the time of their initial diagnosis. Because of this aggressive behavior, the median survival time (time at which 50% of dogs are still alive) for digit melanomas is only about 12 months.
Malignant skin melanomas in dogs
Dogs with malignant dermal melanomas that are smaller than four centimeters have a better median survival time (MST) than dogs with larger tumors. In fact, the MST for dogs with tumors smaller than four centimeters is roughly 12 months versus only four months for those with larger growths. Likewise, the two-year survival rate for dogs with small tumors is about 46% as compared to 0% for those with large tumors.
Unfortunately, for tumors that do recur, the prognosis is poorer than it was for the original tumor.
Lean on your dog’s veterinary team for support
Finding out your dog has malignant cutaneous melanoma can feel overwhelming. It’s understandable to have lots of questions about which treatment option might be best for your dog. You may also wonder if pursuing treatment even makes sense for your dog’s quality of life.
If you have doubts about treatment, speaking to a palliative and hospice care veterinary professional or veterinary oncologist may help ease your mind. They can explain the care your dog will need in the coming weeks or months.
You know your dog better than anyone, and that bond will guide you to make the best decision for your beloved companion.
Has your dog been diagnosed with a skin or paw melanoma?
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