Sarcoids are, at best, ugly skin tumors that detract from a horse’s aesthetic appeal and economic value. At worst, they’re aggressive lesions that don’t respond to treatment, or come back with a vengeance, and interfere with tack placement. But what exactly is a sarcoid?
Sarcoids make up 20% of all neoplasms (abnormal tissue growth) in horses and are the most commonly diagnosed skin tumors in horses. In fact, sarcoids make up a reported 36% of all equine skin tumors.
Veterinarians and researchers have long surmised the cause of sarcoids in horses, with the general belief being that they’re associated with the bovine papillomavirus (BPV). Recent European-based research has added credence to that hypothesis, suggesting BPV variants have become adapted to horses and are probably the cause of most sarcoids.
While the transmission route of sarcoids is unclear, a 2016 study led by researchers at Cornell’s College of Veterinary Medicine found that blame might rest on, at least partially, genetic differences in immune function between horses. The study mirrors findings in humans that show some people have a genetic susceptibility to human papillomavirus, which can cause cervical and other cancers.
The 6 Types of Sarcoids
- Fibroblastic: Fleshy masses that might bleed easily and/or have a moist or hemorrhagic (prone to bleeding) surface.
- Occult: Often-circular, or nearly circular, flat, gray, hairless, and persistent.
- Nodular: multiple, discrete, solid nodules of variable size, which might ulcerate and bleed.
- Verrucose: “Warty,” gray, or crusty and might contain small, solid nodules, possible surface ulceration; well-defined, or covering large, ill-defined areas.
- Malevolent: A rare, aggressive tumor that spreads extensively throughout the skin.
- Mixed: Two or more types.
Common Sarcoid Locations
Sarcoids can develop anywhere on the body, but are usually located on the:
- Paragenital region
- Ventral thorax
- Abdomen
- Head
They are most frustrating for horse owners when they occur where tack is usually placed, such as at the girth or near the poll.
Diagnosing Sarcoids in Horses
Veterinarians can definitively diagnose sarcoids via biopsy. However, the act of sampling the tumor can sometimes cause it to grow worse. So diagnosis is often done based on the tumor’s location and appearance. The horse owner must make a decision as to whether or not it’s better to chance a possible worsening of the tumor to get a definitive diagnosis or presumptively treat the tumor with the risk that it isn’t actually a sarcoid.
Sarcoid Treatment
Sarcoids tend to be notoriously difficult for veterinarians to treat. They often return worse (larger and more aggressive) than the original tumor. Treatments traditionally have included:
- Surgical excision, with a 36-50% success rate and a 50-64% recurrence rate.
- Cryotherapy (freezing), with 60% success rate.
- Interstitial brachytherapy (radiation), with a success rate of anywhere from 50% to 100%.
- Chemotherapy (cisplatin), which researchers performed with 96% success in one study.
- Imiquimod topical antitumor medication that works as an immune response modifier, which results in about 56% remission.
- Topical bloodroot powder and zinc chloride solution paste, with a 56% response rate.
A University of Pennsylvania School of Veterinary Medicine (PennVet) study looked at treating sarcoids with autologous tumor cell vaccination, a promising option for treating cancers in various species. In this modality, a therapeutic agent is produced by isolating tumor cells from an individual, in this case a horse. The tumor cells are processed into a vaccine, which is then administered to the individual from whom the tumor cells were isolated. The PennVet team evaluated 18 horses with sarcoids that underwent the procedure, 16 of which were available for follow-up. Ten months later, 75% of the horses had a decrease in the number of sarcoids, and nearly 69% resolved completely.
Related Reading: Navigating 4 Common Horse Skin Issues
This article originally appeared on TheHorse.com.
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