Animal Cancer Update – Melanoma

Melanomas are relatively common tumours in dogs, but rare in cats. In both species they can range in behaviour from benign (harmless) to malignant (potentially fatal). For many animals with a melanoma of the skin, surgical removal is curative. The most accurate way to predict the behaviour of a skin tumour is to have a sample sent to the laboratory. Melanomas in locations other than the skin, such as inside the mouth in dogs, or in the eyes of cats are generally more aggressive than the skin form. There are many ways we treat patients with melanoma:

1. Surgery. This is the best first-line therapy, and is usually successful in preventing the tumour growing back at the same site. Unfortunately, there are no tests available that detect the tumour elsewhere until the disease is very advanced. In general, if the tumour appears malignant at the laboratory or occurs in a dog’s mouth or cat’s eye, it usually has already spread elsewhere in the body, and most often to the lungs, even though it may not be visible on x-rays for some time.
2. Intralesional chemotherapy. Injecting chemotherapy drugs into the tumour reduces the tumour to the micropscopic level at its original site in about half of all cases. The doses used are too small to cause any side effects, and generally only require sedation and local anaesthetic. Most commonly, 4 treatments are given, each a week apart. Not all patients are suitable for this treatment.
3. Systemic chemotherapy. This form of chemotherapy is used to treat the whole body and hence fight cancer wherever it has spread to. The way in which this is done in animals results in no serious side effects in most patients. On average, treatment lasts 2 months.
4. Vaccination. There is now a vaccine available in the USA which can help dogs with malignant melanoma. Its success is variable but it does appear to result in a durable period of control for many dogs. It works by training the immune system to fight the cancer. It is not available at present outside the USA.
5. Nutritional changes and pain control. There are several changes that can be tailored to individual patient’s diets to improve quality of life. Pain control can be helpful in animals with advanced disease even if they do not show signs of pain.