Cutaneous Melanoma in the Grey Horse

Abstract: 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. The most common areas for primary cutaneous melanomas are underneath the tail, the peri-anal region, different sites of the head and on or close to the genitalia. Common sites for metastases are e.g. lymph nodes, blood vessels, the peritoneum, the spleen, capillaries of the lungs, skeletal muscle, the liver, the parotid salivary gland, bone and bone marrow.Studies of the DNA from grey horses with and without cutaneous melanomas have shown a correlation between certain genotypes and the likelihood of developing cutaneous melanomas. This could explain why grey horses are much more probable to develop these tumors than horses of other colors.