Melanoma in Dogs

Malignant Melanoma Vs. Melanocytomas

Malignant melanoma affects melanocytes, which are cells on the skin that contain melanin, the pigment that is responsible for the color of the skin.

Most cases of malignant melanoma in dogs are in the mouth or mucocutaneous junctions. These are parts of the body where non-haired and haired areas meet, such as the lips and vulva. Malignant melanoma can also develop on the dog’s nail bed. At least 10% of the cases are found on areas of the body that are covered with hair. Being malignant, these tumors are extremely fast growers and have higher risks of metastasizing or spreading to major organs of the body, such as the lungs and liver.

Benign tumors called melanocytomas can also develop in pigmented cells of dogs. Unlike malignant tumors, these tumors don’t metastasize or spread to other areas of the body. Melanocytomas are often found on hairy parts of the dog’s body.

What causes melanoma in dogs?

The reason for the development of melanomas has not been fully established. Experts, however, have seen a link between genetic factors and the occurrence of melanoma. Also, trauma or persistent licking of a particular spot on the skin may stimulate cells to multiply which can increase the likelihood of cell mutation during the process of division, which can eventually lead to their becoming malignant.

Melanoma should always be one of the considerations for any mass that is found in a dog’s mouth. A biopsy will confirm if it’s melanoma or other forms of cancer.

Take note that not all types of skin cancer in dogs are a result of sun exposure. But when it’s caused by sun damage, it usually affects areas of the dog’s body with little or no hair, such as the nose and ears. Also, light-colored or thin-haired dogs tend to be more at risk of sun damage over their entire bodies.

Melanoma in dogs is very aggressive and frequently undergoes metastasis (spread to other areas of the body). It represents about 4% of all tumors diagnosed in dogs. It’s also the most common mouth tumor and the second most common toe/paw tumor in dogs. Even with treatment, local recurrence and metastasis tend to occur frequently.

Signs of Melanoma in Dogs

At first, melanomas in dogs appear as pigmented growths that may bleed or ulcerate as they increase in size. There are, however, melanomas that are pinkish in color; these are referred to as being “amelanotic” or without dark pigment.

Melanomas usually develop in the following areas of the body:

• Mouth - gums, lips, palate
• Foot - including the junction of nail beds and paw pads
• On hair-covered skin anywhere on the body
• Within the eye - cases are very rare

Most melanomas in the mouth and many in the nail bed are malignant, while many tumors on haired skin and within the eye are benign.

Is my dog at risk for developing melanoma?

Melanoma can develop in any breed of dog. However, some breeds, like Chow Chows, Cocker Spaniels, Poodles, and Schnauzers tend to have a higher prevalence.

Diagnosing Melanoma in Dogs

Diagnosis of melanoma in dogs is made possible by the following procedures:

• Oral examination
• Assessment of lymph nodes by cytology or biopsy
• Chest x-rays
• CT scan
• Abdominal ultrasound

When staging for malignant melanoma, your veterinarian or veterinary oncologist will consider the size and whether it has metastasized to adjacent lymph nodes or the lungs.

Prognosis

The prognosis of melanoma in dogs depends to a large extent on the stage. As melanomas in dogs increase in size, the prognosis with surgical removal decreases.

• Stage 1: The tumor is less than 2cm and there is no metastasis. The average survival time is 15-18 months if surgical removal is performed.
• Stage 2: Tumors are greater than 2cm. The average survival time is 6 months if surgical removal is performed.
• Stage 3: Tumors are larger than 4cm and metastasis to lymph nodes may be present. Survival time is roughly 3-4 months with surgery.
• Stage 4: Cancer has already spread to the lungs. Very poor prognosis; average survival time is 1-2 months.

Treatment Options for Melanoma in Dogs

The treatment options for melanoma in dogs include the following:

• Surgery
• Chemotherapy
• Radiation
• Intralesional therapy
• Immunotherapy

The treatment regimen for melanoma in dogs is focused on controlling the growth of the tumor, as well as dealing with metastasis concerns.

Local control of the tumor involves surgery and/or radiation treatment. These are the most common options that are generally practiced.

There is a melanoma vaccine for dogs that is often recommended in conjunction with surgery and/or radiation. This can help prevent the possibility of future metastasis. The vaccine is formulated for dogs with stage II or III or oral melanoma after initial local control. A 2015 study on the use of the melanoma vaccine in 38 dogs after local control had been achieved, showed a significant increase in the survival times in dogs with oral and digit (toe) melanoma. The results of the study showed that a combination of surgical removal and vaccination can significantly improve the prognosis.

If your dog has been diagnosed with malignant melanoma, you should ask your vet about the vaccine and other treatment options.

Since chemotherapy does not consistently achieve favorable responses against malignant melanomas, it is usually reserved for tumors that have recurred or started to spread to other parts of the body.

Read more:

Warning Signs of Cancer in Dogs

Should I worry about a cyst on my dog’s skin?

Mast Cell Tumors in Dogs

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