Equine sarcoids.

Sarcoids, the most common tumor of the horse, are fibroblastic, wart-like skin lesions that show variable manifestations. They are often invasive and recurrent, although they do not fulfill all criteria of malignancy. Due to their anatomic location, these tumors can sometimes cause loss of use of the horse. There is very strong evidence that sarcoids are caused by viruses closely related or identical to bovine papilloma viruses, and genetic studies have shown associations between genes in or near the equine major histocompatibility complex (MHC) and susceptibility to sarcoid. Several types of treatments have been successful in treating sarcoids, although the response to therapy is not consistent. Current treatment of sarcoids primarily involves antitumor therapy, but the development of preventative measures in the future may be directed against the causative papilloma virus. Sarcoid continues to be an important clinical entity for the equine practitioner.