Page 80 - Speedhorse May 2019

A sarcoid before treatment (left) and during treatment (right).
“A lot of the sarcoids around the eyes involve the eyelid, which means you can’t surgically remove them, so we use some kind of localized treatment like BCG or cisplatin which is a type of chemotherapy.”
The drug that’s been reported to have the most success is called platinol or cisp-platinum in oil, but requires special handling so not all veterinarians use it. The person administer- ing it needs to wear gloves, protective clothing and use special disposal. It also requires repeat injections of the area using a special needle sys- tem. According to some reports, this treatment can be 100% effective. This drug should not be used in breeding animals, however, or any horses with impaired kidney function.
Radiation therapy is used on some sarcoid lesions, but only a few hospitals offer this form of treatment. “Although this is an effective treatment option, the drawback is that the horse usually needs to be anesthetized for each treatment so owners generally shy away from it.” Chemotherapy has also been found useful in treating equine sarcoid.
“Most of what I do is surgical removal fol- lowed up by chemotherapy, since I am generally dealing with growths that other people have tried to put BCG on, or 5FU (Fluorouracil, which is a medication used to treat cancer),
or Imiquimod cream (which is used to treat certain types of scaly growths on the skin or to treat superficial basal cell carcinoma), or some other topical treatments that merely poked the bear. If people are using those sorts of things, however, it’s probably because they’ve had some success doing it with some cases. If you read the literature, this seems to be true,” says Smith.
The size of the lesion makes a difference in how it is treated. “Probably no treatment would work very well for a really large fibroblastic mass. Most of what we know about sarcoids goes back to their cause (bovine papilloma virus) and treatment may not be as effective as we’d like it to be,” he says.
The virus enters the skin via an opening in the skin, such as trauma or fly bites. “The virus may lie dormant for many years in the skin. Studies have shown that biopsies from normal horses (30 to 40%) are positive for the virus. More than 90% of sarcoids sampled contain bovine papilloma virus, so we know it’s a big player.
“Sarcoids in general are not very well circumscribed masses. The sarcoid has little fingers that go in all directions. They are simi- lar to the root system of a tree in that some of it is beneath the surface. The tumor and/or virus infiltrates a wide area beneath the surface of the skin. If you chop a tree off at the base, you haven’t removed the root system underneath. The reason there’s a lot of treatment failure is that many people simply chop off what they can see. They don’t treat the root system under- neath, and the sarcoid may regrow.
“Unlike melanomas, which usually are very well circumscribed (you can tell the limits of these growths and can remove them), with sarcoids
we very rarely get all the margins. If you don’t treat the base, they will just recur. One reason they recur is that the papilloma virus is there, surrounding the sarcoid. Since you merely excised it and created inflammation, the inflammation stimulates more growth. In horses that have the virus in their skin, we think that all they need is a traumatizing event to get it going,” he says.
The virus may have entered the horse’s skin years earlier - even 10 to 15 years before - and then the horse starts getting sarcoids. “This is what we think happens with most of the cases that occur on the limbs. They are often get- ting bumped, scraped or nicked, which might stimulate the virus to create the growth. So when you go in there surgically and do that, you cut down the tree but forgot to remove the root system and it regrows.
“That’s why when people ask if I want to biopsy a growth to see if it’s a sarcoid, I tell them absolutely not. Either I am going to remove all of it and treat the base to remove the
roots as well, or I am going to just watch it to see if it grows. If it starts to enlarge, that’s when you want to remove all of it. If you traumatize it, it just turns it into a more aggressive form.
“Another reason some sarcoids recur after treatment is that most practitioners don’t have use of a laser or other tools that can excise tumors without spreading them by inoculat- ing the tumor bed. When you cut the tissue with a blade (unless you can get huge margins around it, which rarely happens for me because I am usually doing the very large sarcoids),
you inoculate the surrounding tissue with the virus. Even if you resect the tumor with what you think are adequate margins, you are still likely going to be cutting through sarcoid tis- sue somewhere along the way. You are simply inoculating the whole area again, so the sarcoid is more likely to recur.
“Sarcoids are likely to recur, regardless of treatment selected. Probably the most effec- tive treatment is surgical excision followed by some sort of chemotherapy, whether cisplatin, carboplatin injections or radiation. Most people inject the chemotherapy drug of choice with sesame oil, which increases the length of
Many warts that occur in older animals, such as aural plaques (warts in the ears), are caused by equine papilloma virus 2. Those do not go away and some can progress into squamous cell carcinoma.
78 SPEEDHORSE, May 2019
EQUINE HEALTH