Equine Melanoma in Horses

Melanomas are cancerous growths most commonly associated with mature grey horses, the majority of affected animals will enjoy long and successful lives and careers with the masses having little direct effect on their quality of life.

The tumours are usually benign and grow slowly, however, in a small number of horses, they can become locally aggressive and may migrate to multiple sites within the body. Approximately 80% of grey horses older than 15 years will develop a growth.

Melanomas develop when cells that contain the dark pigment melanin (melanocytes) proliferate and multiply. The majority of equine melanomas grow in the skin and are readily visible. They are most often found as clusters of firm, dark nodules or as solitary black bumps.

The most common locations include the undersurface of the tail; the perianal region, and the external genitalia. They also frequently occur in the jaw region, the neck, the eyes, and the ears. Less commonly the eyes and limbs can be affected.

Researchers have tracked both grey coat colour and high melanoma risk to the same mutation on a single gene, which explains why these tumours appear so often in grey horses but so rarely in bay or chestnut Coloured horses.