By: Dr. Lydia Gray
Melanomas are skin tumors. Specifically, they result from abnormal growth of the skin cells that make the pigment melanin. Melanomas are roundish, black, firm nodules most commonly found under the tail, around the anus, below the anus (the perineum), on external genitalia, and in various other sites around the body. Approximately 80% of all gray horses will eventually develop melanomas while the tumor only occurs in about 30% of non-gray horses. However, when melanomas occur in a horse that is not gray, the tumor tends to be a more aggressive form of cancer.
There is controversy over whether melanomas are malignant or benign, but most veterinarians agree that since the tumors will continue to grow, the earlier they are treated the better. Depending on the location of the melanoma and other factors, treatments may include surgery, cisplatin (anti-tumor) injections, oral cimetidine (an anti-ulcer medication), radiation, laser and other methods.
The most common breeds to develop melanomas are Arabians, Lipizzans and Percherons. While there is no way to prevent these tumors from forming, owners can improve the outcome by contacting a veterinarian as soon as any change in the skin is noticed.