Melanoma in Dogs

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Cancer is scary for both humans and pets. With improved medicine, food, and general quality of life, dogs are living longer than ever, but that has also put them at risk of age-related diseases, like cancer. About 6 million dogs are diagnosed with cancer each year. According to the Veterinary Cancer Society, cancer is responsible for about 47 percent of all deaths in canines.

According to studies by the Animal Tumor Registry of Genoa, Italy, mammary cancer is the most frequent of all cancers, accounting for about 70 percent of all cases of cancer. In female dogs, mammary cancer and non-Hodgkin’s lymphoma are the most prominent, while male dogs more commonly deal with non-Hodgkin’s lymphoma or skin cancer.

Skin cancer is often the easiest to spot with the formation of melanomas on your pup’s skin. This article will take a closer look at melanoma, what it is, signs to look out for, and tips for treatment and prevention.

What is a Melanoma?

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Melanoma is a type of cancer of the skin the begins in melanocyte cells. Melanocytes are the cells that create the pigment melanin, responsible for the color of a dog’s skin, fur, and eyes. Melanocytes are also responsible for creating moles, which is where many melanomas tend to form. When these melanocytes begin to abnormally grow out of control, they may form melanomas.

The various types of melanoma are identified by their location and include:

  • Cutaneous melanoma (appearing on the skin)
  • Ocular melanoma (appearing on the eyes or eyelids)
  • Oral melanoma (appearing anywhere around the mouth or oral cavity)
  • Subungual melanoma (appearing on the nail bed)

Melanomas are categorized as benign or malignant. Benign melanomas, which are also called melanocytomas, are generally harmless with a very low risk of metastasis, though depending on where they form, they can be locally invasive or irritating.

However, malignant melanomas can readily metastasize, spreading to various parts of your pup’s body, particularly the lungs and lymph nodes. This can present some serious health issues that could potentially be life threatening.

Identifying Melanoma in Dogs

Benign melanomas generally only appear on the surface of your dog’s skin. They look like firm, round, raised masses that are darkly pigmented. These can measure from a quarter of an inch to two inches in diameter and occur most often on a dog’s head, back, or paws. They often appear as black, gray, brown, or red in color.

Malignant melanomas appear most often in the mouth of mucus membranes, though they can occur and spread just about anywhere on your pup’s body, including the pads of the feet and in toenail beds. A malignant melanoma tends to have a higher concentration of melanin, creating an abnormally dark color, though some malignant melanomas do not have that characteristic dark color.

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Potential Causes of Melanoma in Dogs

Much like with human cancer, not many people know what causes melanoma and other cancers in dogs. Genetics seem to play the primary role. Some research suggests that physical trauma or constant licking of a spot on your dog’s body may increase the chances of cells multiplying, potentially giving those cells a greater opportunity to mutate and become cancerous.

For humans, one of the biggest causes of skin cancer is sun exposure. However, excessive sunlight does not seem to cause melanoma in dogs. In fact, dogs with brown, black, or otherwise dark fur seem to have a higher chance of developing melanoma than their lighter-furred cousins.

You should still be aware of the amount of sun your dog gets as too much sun exposure can cause a different form of skin cancer known as squamous cell carcinoma.

Risk Factors of Melanoma in Dogs

Melanoma is most common in older dogs, usually at the age of 9 or older. Malignant melanomas are also more likely to appear in the toes or toenail bed of black dogs.

Certain dog breeds are more predisposed than others. These breeds include:

That said, melanoma may potentially affect any dog, usually between 5 and 11 years old. 

Signs and Symptoms of Canine Melanoma

The scary part about most melanomas is that they don’t generally show any immediate, systemic signs of illness until the cells have already metastasized to other organs and parts of your dog’s body. Often the most prominent sign of melanoma is the presence of the darkly pigmented tumors detected by you or by a trained veterinarian during a regular checkup.

Melanomas in your pup’s skin are easy to spot. These may simply appear as raised sores or dark bumps. They are more often than not benign and rarely spread, cause problems, or pose severe symptoms.

Oral melanomas look like raised masses in the mouth. While they are normally found by routine checkups and dental examinations, oral melanomas are generally accompanied by excessive salivation (known as ptyalism) and sudden, noticeably bad breath (known as halitosis).

Melanomas in your dog’s nail bed are only moderately metastatic, but they can still be invasive. Melanomas in nail beds or toes often lead to:

  • Swelling
  • Limping
  • Lick or chewing at the affected area

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Canine melanomas occurring in the feet are also prone to infection, often leading to misdiagnosis.

Melanomas in or around a dog’s eyes are usually benign and rarely have a chance of metastasizing. If your dog has ocular melanoma, you may notice:

  • A mass in the eye or eyelid
  • Redness in the eye
  • Cloudy eyes
  • A change in the eye’s general appearance
  • Darkening of the iris
  • Swelling in or around your dog’s eye
  • Ocular pain
  • Impaired vision, which may manifest as your dog bumping into objects in familiar settings or having difficulty navigating unfamiliar areas
  • Twitching muscles around the eyes

Diagnosing Melanoma in Dogs

Diagnosing a melanoma generally starts with a simple physical examination. The lumps and bumps characteristic of melanoma are easy to spot by veterinarians and pet owners. Your vet will likely perform an assessment, which may include urine and fecal samples.

From there, if your dog’s vet suspects melanoma, they may proceed with microscopic evaluation of cells and tissue samples. The most common of these procedures involves an FNA, or fine needle aspirate. During this procedure, the vet will insert a needle into a suspicious mass or lump and pull out affected cells. These cells are placed onto a glass slide and examined closely.

Your vet may then take a biopsy of the mass. This involves taking an actual piece of tissue from the lump instead of just a cell sample. These are performed under sedation or general anesthesia. The tissue taken during a biopsy is sent to specialized labs for more precise evaluation and processing. From the biopsy, the vet can determine how likely the melanoma may spread or invade other organs.

Other potential tests for melanoma in canines include:

  • Fine needle aspirates of lymph nodes nearby the mass to determine if the cells have metastasized into the lymphatic system
  • Chest x-rays to see if the cancerous cells have spread to the lungs
  • Ultrasound tests on the abdomen to determine if any other part of the dog’s body has been affected

It should be noted that the technology and tests used to evaluate and diagnose canine melanoma are constantly evolving to better identify the different stages of the melanoma.

Treatment for Melanoma in Dogs

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Treatments for melanoma in dogs generally depend on the location of the tumor and the extent to which it has spread, but surgery tends to be first step. Often, even benign melanoma are removed, partly because the area may be bothersome to the dog, and partly to avoid the chance of it becoming malignant. The surgeon will usually make larger margins to prevent chances of regrowth or spread. A pathologist can examine the removed mass to determine if the cancerous cells have spread and to what extent.

If the melanoma cells have spread or could not be removed entirely, your dog’s vet will likely use radiation therapy. With radiation therapy, melanoma has been shown to go into remission about 70 percent of the time. Chemotherapy may also be used, either on its own or in conjunction with surgery and radiation therapy.

The USDA conditionally licensed a vaccine in 2007 that could potentially treat canine melanomas. The vaccine causes the immune system to attack and reject tumor cells, prolonging overall survival times. However, research on this vaccine’s effectiveness is ongoing.

Malignant melanoma is highly aggressive and should be treated immediately. Depending on the location, malignant melanomas will require surgical removal of the area and surrounding tissue, including bone. This may mean removal of the dog’s jaw in the case of oral melanomas or amputation of the toe in subungual melanoma. Thankfully, reconstructive surgery can help to rebuild those areas.

Dogs that have surgically removed benign tumors have a very good prognosis. The outlook for dogs with malignant melanomas depends on the stage at which the melanoma has been caught and treated.

Preventing Melanoma in Dogs

There isn’t a realistic or reliable means of preventing melanoma as vets still are not sure of the precise causes of melanoma. However, with early detection, you and your vet can better increase the chances of ensuring a long healthy life for your dog.

Keep an eye out for dark nodules or masses on your pup’s body, eyelids, and paws, particularly if your dog is one of the breeds predisposed to melanoma. Familiarize yourself with the potential symptoms and give your dog a routine examination to identify any strange bumps, lumps, or masses. It’s easy to do and your dog will enjoy the pets and belly rubs.

Above all, as your dog’s owner and best friend, you probably know your pup better than anyone and can determine when something just doesn’t seem right. If your pup is acting strangely or is consistently licking at the same spot on their body, make an appointment with your vet. It’s better to be safe than sorry.

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