An equine melanoma is a tumor that results from the abnormal growth of melanocytes in horses. Unlike in humans, melanomas in horses are not thought to be caused by exposure to ultraviolet light. Melanomas are the third most common type of skin cancer in horses, with sarcoids being the first most prevalent and squamous-cell carcinoma being second. Melanomas are typically rounded black nodules that vary in size and are usually found underneath the dock of the tail, in the anal, perianal and genital regions, on the perineum, lips, eyelids, and sometimes near the throatlatch.