Melanomas are tumors that arise from the transformation of normal melanocytes; which are the pigment-producing cells located not only in the skin, but also throughout the body. While these tumor occur naturally in all mammals, they are among the mostcommon tumors noted in horses comprising between 3.8% to 15% of all skin tumors, second only to sarcoids. According to some studies the incidence of these tumors in horses may be increasing in parallel with the reported increased incidence of the diseaseseen in humans. Although it has been suggested that a gender predisposition exists, no clear predilection on the basis of gender has been established. In contrast, while melanomas have been diagnosed in all breeds and colors of horses a marked predisposition has been extensively reported in grey horses with prevalence rates reaching as high as 80% in older animals.
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