Sarcoids are a type of skin tumor sometimes occurring on the skin of horses. Sarcoids are a benign tumor caused by the Bovine Papilloma Virus (yes, as in “cow”) that has invaded the skin of a horse. The virus goes undetected by the horse’s immune system and begins to slowly grow and gain a blood supply. Sarcoids can eventually grow very large. They usually start out looking like a flat, hairless patch about the size of a quarter. After a long while (sometimes years) they start to get larger, round, and bloody. They never invade into the body of the horse so they do not ever
mean a horse needs to be euthanized because of them. However, they can become an ugly problem cosmetically. They can be treated with surgical removal, freezing, or various creams like 5-florouracil or Xxterra. All of these treatments have about a 75% success rate. In very large, recurring cases, a newer technique has been used. The idea of this treatment is to expose the horse’s immune system to the virus with tissue from the tumor of the same horse. In this procedure (done at the farm), a large tumor is removed and pieces are cut up into little squares that are frozen in liquid nitrogen and implanted into the horse’s skin under the mane.
This exposes the tumor causing virus to the horse’s immune system. In most cases, the horse’s immune system then attacks the tumor cells still in its body. This treatment is sometimes used for large recurring tumors, where the skin cannot be closed easily after surgery, or if the horse has multiple tumors all over its body.