Melanoma

What is melanoma?

Melanoma is a benign or malignant tumour made up of melanocytes, which are pigment-producing cells. Melanoma is more common in male dogs and those with dark pigmented skin. Some breeds including Scottish Terriers, Black Labrador Retrievers, Cocker Spaniels, Gordon and Irish Setters, Chow Chows, Doberman Pinschers and Golden Retrievers seem to be more prone to this form of cancer.

Depending on the area of the body where the melanoma develops, the cancer will tend to be benign or malignant. Melanoma that develops on the skin tends to be benign while melanoma of the mouth, toe or toenail bed is usually malignant and spreads quickly.

With respect to melanoma of the mouth, the size of the tumour will affect survival times. This form of melanoma is staged to help veterinarians determine the best course of treatment.

Stage I: tumour size is less than 2 cm in diameter (survival time: about one year)
Stage II: tumour size is 2 – 4 cm in diameter (survival time: about six months with surgery)
Stage III: tumour size is 4 cm or larger or any tumour with local lymph node involvement (survival time: three months with surgery)
Stage IV: any tumour with evidence of distant spread (survival time: case by case)

Melanoma of the toe or toenail bed is more common in black dogs and this form of cancer is very aggressive, with about 40 per cent of cases having spread by the time they are diagnosed.

Causes of melanoma

Although sun damage has been show to cause melanoma in people, the cause of melanoma in dogs is less clear, since many of the melanomas occur in areas not directly exposed to UV light.

What are the symptoms of melanoma?

The most common symptom of melanoma of the mouth is noticeable swelling. Other symptoms include increased salivation, facial swelling, weight loss, bad breath, noticeable pain, inability to eat, dropping food from the mouth and loose teeth. Tumours in the mouth may be black, pink or white in colour.

Symptoms of melanoma of the toe include swelling of the toe, loss of the toe-nail and/or limping on the leg of the affected toe. These tumours are usually black in colour.

How is melanoma diagnosed?

Melanoma is diagnosed by fine-needle aspiration — inserting a small needle into the tumour and removing some cells for evaluation. Sometimes a biopsy is necessary if the results from the aspiration are inconclusive.

Veterinarians advise that all dogs diagnosed with melanoma should have their lymph nodes and lungs checked to see if the cancer has spread. This is done through aspiration of the lymph nodes and an x-ray or CT scan of the lungs. Sometimes the abdominal organs such as the spleen or liver are checked through ultrasound to see if the cancer has spread to these areas.

Treatment and prognosis

Surgery to remove the tumour is the recommended treatment for melanoma. In some cases, it may be difficult to remove a tumour in the mouth without also removing bone. However, most of these dogs will still be able to eat, drink, chew and play with their toys. For melanoma of the toe, the entire toe will usually be removed along with the tumour.

If the tumour cannot be completely removed or if the cancer has spread to the local lymph nodes, radiation therapy is used. About 70 per cent of dogs treated with radiation therapy after surgery, go into remission. Unfortunately, cancer often reoccurs.

Chemotherapy is sometimes used in the treatment of melanoma when the tumour cannot be removed surgically; if radiation therapy has proved unsuccessful; or when the cancer has spread.

A canine melanoma vaccine called Oncept, produced by Merial, is available through veterinary oncologists and is used for dogs with stage II or stage III melanoma of the mouth, to help extend survival times. The vaccine works by stimulating the dog’s immune system to kill the melanoma cells.

The average survival time for dogs with malignant melanoma without any treatment is only a few months. Dogs with melanoma of the mouth who have been successfully treated with surgery, with or without radiation therapy, live about a year and a half to two years and some even longer. Dogs with melanoma of the toe live about one year after surgery alone and longer with additional treatment.

As with many cancers, early diagnosis is key to successful treatment. Grooming your dog on a regular basis can help detect any irregularities on the skin, toes or in the mouth.

 


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This page has been reviewed by our Panel of Experts for accuracy. Our Panel of Experts is comprised of practitioners with varying specialties and perspectives. As such, the views expressed here may not be shared by all members of our Panel.

The content on this website is for informational purposes only and is not intended to be a substitute for professional veterinary medical advice, diagnosis or treatment.