Sarcoid is the most common cancer of horses. I suppose I should say on horses, because sarcoids are skin tumors. They can grow to be very large, but they don’t spread to internal organs. Although common, I don’t think I’ve ever been called out specifically just to look at one. That’s because at first they usually don’t look very impressive. As a result, owners tend to wait until their vet is on the farm looking at something else. Then it’s usually: “as long as you’re here, would you checking out this skin bump?
Sarcoids don’t follow any of the usual rules for cancer, and as much as they have been studied, we really don’t know exactly why they act as they do. They aren’t like other cancers. First, they tend to occur in younger and not older horses as you would expect. Secondly, they appear in a wide variety of shapes. Most of the ones I see are what we call nodular, just a hairless bump on the skin. Initially they can be mistaken for a tick bite. Sometimes, instead of a smooth surface they are wart like with fringy fingers. Others are totally flat, and look like a piece of old bumpy leather pasted on the skin. Rapid growing ones may look just like a cauliflower, and can get every bit as big. Because of their size these stick way out from the skin and bleed when they get bumped. Some grow on stalks. I have seen a few that are a crazy mixture of all these types. An internet check will bring up photos of types of sarcoids. Google “horse sarcoid images.”
Sarcoids are often found where there has been a wound or trauma. For example, a horse that has had many IV’s may develop a sarcoid on the skin over the jugular vein. Despite the skin damage that saddles can cause, I’ve never seen one on a horse’s back.
When pathologists study sarcoids they often find the DNA of the bovine (cattle) papilloma virus deep inside. It is thought that flies carry the virus from cows to horses. When I see a sarcoid and question the horse’s owner, I am usually told that the horse has had contact with cattle at some point.
The state of a horse’s immune system when exposed must also be important, because horses that get sarcoids tend to get more. Their herd mates might never have one.
Veterinarians will back away if you start a conversation about doing a biopsy of anything that looks like a sarcoid. When cut into, they tend to start growing more aggressively. Even if it’s a small one and you make wide incisions in order to get every cell, there is a pretty good chance of the sarcoid coming back bigger. So, as a treatment, surgical removal is usually not a good idea.
In general, sarcoids are not a great health risk, but if they are growing on areas of the body that apt to get knocked about, its best to get rid of them. There are many treatment options, which tells me that nothing works all the time. Some sarcoids disappear without any treatment at all. There are also medications which can be injected into sarcoids that will cause them to shrink and hopefully finally go away. The two most popular are Cisplatin and BCG. Typically, you have to inject them many times over a period of weeks. Sometimes the injections cause local inflammation and make the area painful.
I have had good luck using liquid nitrogen sprayed on the nodular types to kill the cells. Mostly this has worked with little recurrence. There are also some veterinary herbal preparations. The most popular is Xxtera. The active ingredient of this ointment is blood root, a flowering plant whose extract has been used for skin growths since colonial times. A small amount applied daily will cause smaller sarcoids to shrivel up, but it may leave an unsightly scar.
A few topical medicines made for people have been used on equine sarcoids. Examples are Aldara, 5-Fluorouracil, and Acyclovir. More are always being tried. Some work by affecting the immune system, others are antiviral. Intense local reactions may occur. These human preparations are usually quite expensive. Lasers have been used with some success. The literature reports that radiation therapy may be the most effective treatment, which means several costly trips to a university or major surgical center.
There are all kinds of sarcoid home remedies that have been tried by horse owners. One of the most interesting is the daily application of Crest toothpaste. You’ve got to wonder how anyone came up with the idea. Some feel that the fluoride in the toothpaste is what shrinks the sarcoid. An on-line report claims that fluoride mouth wash sprayed on a troublesome sarcoid in the groin made it disappear. That one shows colored photos which show the tumor shrinking. Would it have gone by itself? Perhaps. Certainly it would be worth a try, and couldn’t hurt.
Equine veterinarians have become pretty adept at identifying sarcoids by their appearance. It’s never an emergency, but the next time your vet is out, question if that newest bump might be a sarcoid. Generally, sarcoids tend to be slow growing and not a cause for alarm.
Dr Jefferson is the founding veterinarian of Maine Equine Associates. He can be reached at www.MaineEquineAssociates.com His previous articles that have appeared in the The Horse’s Maine are archived on that site.