Melanomas are tumors of the melanin, pigment-producing cells. They’re common in gray horses, usually first appearing under the tail. However, they can be found on any horse. Because they usually spread slowly, most horses die for unrelated reasons, and routine treatment isn’t needed.
However, if your horse has melanomas you need to know that some complications have been reported:
• Ulceration: This is the most common complication and occurs in tumors that are irritated, e.g. in high -friction areas. Routine open wound care and, in some cases, surgery or cryotherapy to reduce the size of the tumor in that location are indicated.
• Lameness: Internal spread to the pelvis may result in tumors forming that are large enough to put pressure on local nerves and blood supply. Hind-limb lameness as a result has been reported. Lameness can also result if tumors spread directly into the muscles of the hind limb.
• Paralysis/anemia: Spread into the bones of the spine and the bone marrow of other bones may occur.
• Miscellaneous: Spread to liver, spleen, lung and even brain has also been reported.
• Cushing’s: Melanomas may worsen if the horse develops Cushing’s. The Cushing’s tumor can produce hormones that stimulate melanoma cells.
Melanomas in non-gray horses are more likely to show malignant spread than they are in grays. In grays, the older the horse and the longer melanomas have been present, the higher the chance they’ll spread.