Equine cutaneous melanomas arise much more often in horses with a grey coat color than in horses of other colors. Some scientists have in different studies come to the conclusion that the melanomas are neoplasms which can be classified by examining their histological and macroscopic features. The more defined and demarcated a tumor is, the more benign it tends to be. Other scientists believe that the skin lesions are the result of a pigmentation disorder that is linked to the greying of the coat color. According to this theory, the lesions are not malignant although they have the ability to metastasize.