I would order a jar of clean horse. Two years ago I used it on a sarcoid that popped up on one of my best horses. This is actually an old native American cancer remedy, that many old timers used. The sarcoid on my horse was growing quickly, and looking pretty nasty. A friend of our save me a little of his salve to get started on, then I ordered Clean Horse, which removed it completely in about 1 1/2 weeks. My dad has also used this on suspicious spots on his face that he was having to get burnt off repeatedly by the derm. The person who makes this product is very helpful and can tell you how to use it. Cleanhorse.com. It does work, and these older grays are prone, so I would try to remove it this way, first.
Between my husband and I, we have a good bit of experience with not only healing, but patching up wounds/injuries. People are always trying to send us horses to fix for them. On the other hand, I've seen a couple of horses (that belonged to acquaintances), who had small malignant spots. These friends/acquaintances didn't try the salve, and areas got much worse. So take it for what it's worth. I've found the $50 jar worth every penny.