Melanoma in Horses

August 20, 2007 (published)

If you have ever owned a grey horse, then you are probably familiar with melanomas. Melanomas are commonly malignant tumors in people and non-grey horses but the type of melanoma that commonly occurs in grey horses are considered to be benign. They are commonly seen in grey horses over 10 years of age and in many cases do not cause any problem. In general, I tell clients that these tumors on grey horses are rarely malignant and depending on the area, usually do not cause a problem. However, they can ulcerate and this can lead to an infection and pain for the horse. The tumors generally develop in fairly sensitive areas such as the groin, perineal area, lips and eyelids and can become malignant but this is rare.

Drs. Pillsworth and Knottenbelt report that melanomas on the head can spread to lymph nodes that surround the jugular veins and carotid arteries in the neck, as well as spread to inside the horse's guttural pouches. Because of the physical size of some of the tumors, clinical disease can occur depending on the location of the masses. As an example, if a tumor is located in the spinal cord area, neurological symptoms can occur. Also, tumors in the guttural pouch have been shown to cause a horse to have difficulty swallowing. As far as treatment, removal of the masses while they are small is usually recommended. The drug cimetidine has been shown to decrease the size of some of these tumors in certain cases, but the most successful treatment is removal with a laser or freezing them after a large portion of the tumor is removed surgically. If you have a grey horse with melanomas, consult your vet for treatment options.

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