Battling the equine sarcoid

Sarcoids are the most common tumor in equids worldwide. Any practitioner who sees equid patients has undoubtedly fought the good fight against sarcoids.

As with any condition that has myriad treatment options, no perfect treatment exists. Additionally, the wide range of variables that are present with each tumor (different types, rates of growth, responses to treatment, size, location, horse stabling conditions, horse temperament, owner ability, owner needs, budget, etc) make deciding how to treat sarcoids challenging at best.

These extensive possibilities in tumor variables and treatment options have resulted in a wide array of recommendations and results in the published body of peer-reviewed literature, with described recurrence rates widely ranging from 2% to 80%.^1,2 Certain factors that have been associated with increased risk of recurrence include size of tumors, repeated or prior treatments, and periocular location.³

Although a variety of treatment options can be successful, failure of any treatment method can, and often does, result in the recurrence of a more aggressive tumor. Owners should be informed of this risk when sarcoids are discovered or a treatment option is being pursued.

Excellent healing and cosmetics after treatment of multiple sarcoids of the ear
pinna 6 months prior.

The sarcoids were removed with a CO₂ laser under standing sedation utilizing local anesthesia.

Follow up 5 fluorouracil injections were performed immediately after surgery.

Identifying sarcoids

Sarcoids are cutaneous, fibroblastic neoplasms with a proliferative epithelial component and are classically grouped into 6 types, as follows:

1. Occult: flat and hairless, often circular
2. Verrucous: scab or wart-like appearance, possibly containing small nodules
3. Nodular: discrete, solid nodules that may ulcerate and bleed
4. Fibroblastic: irregular growths with a wet, hemorrhagic, ulcerated surface that typically bleed easily
5. Mixed: a combination of 2 or more types
6. Malevolent: a rare, aggressive tumor that spreads extensively

Managing sarcoids

Mixed sarcoid in the inguinal region of a horse in dorsal recumbency.

Initial treatment of a small sarcoid with a topical treatment resulted in rapid, aggressive growth of the tumor, requiring extensive and prolonged treatment.

Treatment option categories for equine sarcoids include benign neglect, topical, immunotherapy, cryotherapy and hyperthermia, chemotherapy, electrochemotherapy, excision, radiation/brachytherapy, photodynamic therapy, and a combination of these treatments.

Benign neglect

Benign neglect should be considered only in small occult or verrucous tumors. However, sarcoids can remain visibly unchanged for extensive time periods and then suddenly enlarge without warning. Treatment should be considered or discussed with owners in all cases, as treatment of small, less aggressive tumors is typically more successful than addressing a rapidly growing sarcoid.

Excision

This treatment can include sharp/ conventional, electrosurgical, laser, or banding. The use of lasers in tumor excision is thought to be helpful in preventing tumor cell spread through vaporization of cells and by sealing the lymphatics.⁴ Although excising tumors is nothing new, it remains a mainstay in the treatment of sarcoids. Whether performed alone or in conjunction with other treatments, surgical excision typically results in a high rate of treatment success. Additionally, the success rates of most other types of treatments are typically much higher when combined with tumor excision.^1,2 Although there are exceptions, in general, excision with the largest possible margins is recommended no matter the additional route of treatment that is pursued.

Topical treatments

Administered frequently in general practice or by owners, topical treatments are low cost and easy to use. They may be combined with other treatments, like excision, or applied directly to a tumor. Topical treatments can be generally grouped into 2 categories: those that solely irritate the tissue and stimulate the immune system such as bloodroot (Xxterra; Vetline Equine) and those that fight tumors with cell or viral targeting agents including imiquimod (Aldara; 3M Pharmaceuticals) and 5-fluorouracil (AW5; Equine Medical Solutions). Nearly all treatments result in irritation and inflammation of the tissues, with the tumor looking worse before it improves.

Topical treatments can be a cost-effective and successful treatment. However, they likely carry the highest risk of transforming a small lesion into a more aggressive and extensive tumor because of the irritation of the tumor and have been associated with lower treatment success rates.²

Chemotherapy

Local chemotherapy remains a common and successful method of treatment, demonstrating widespread success in treating sarcoids, particularly in conjunction with tumor excision or debulking. Of the chemotherapy drug options, cisplatin and 5-fluorouracil have the most evidence for success against equid sarcoid. Local chemotherapy injection has a good safety margin for the patient, is generally straightforward for a veteri- narian to perform when understanding sedation, and is fairly affordable for the client. However, typically, a minimum of 3 injections should be performed, once every 2 to 3 weeks. At times, this can lead to low client adherence and failure of treatment.

Cisplatin beads can be purchased, although the cost is higher than that
of the injectable agents. These beads can offer slow release but they require small stab incisions for the beads to be placed into tissue dense enough to hold a suture to keep the bead in place. Unfortunately, this can mean that more tumor tissue is left in place to be able to have enough tissue to hold the beads. Topical chemotherapy should be saved for post-tumor removal application as absorption is poor and typically results in treatment of surface cells alone.

Electrochemotherapy

Electrochemotherapy has become very common in referral type practices with high published rates of success and low risk. However, with the added necessity of general anesthesia and a similar success rate to injection of local chemotherapy, it is fairly clinician dependent whether electrochemotherapy is recommended over local chemotherapy injection alone.

Cryotherapy, hyperthermia, and photodynamic therapies

This case demonstrates the risk involved with cryotherapy use. The horse presented for repair of a damaged ear pinna that was resulting in chronic infections in the area where the pinna was collapsing.

The horse had reportedly been treated for a sarcoid with cryotherapy. The cartilage in the pinna was damaged with the cryotherapy, leading to pinna collapse. The linear scar and hairless area ventral to the area of pinna damage was also presumably caused by runoff of liquid nitrogen.

Heat (hyperthermia), cold (cryotherapy), and light (photodynamic therapy: application or injection of a photosensitizing agent followed by light administration) have all been used to treat sarcoids with highly variable success rates depending on individual studies. They represent an effective but nonselective group of treatments, carrying the risk of damage to normal surrounding cells. They all must be used with extreme caution to ensure that damage to surrounding tissue is minimized.

Immunotherapy

Immunotherapy, including mycobacterium cell wall fraction (Immunocidin Equine; NovaVive), live whole-cell Bacillus Calmette-Guerin (TICE BCG; Merck Teknika LLC), propionibac- terial cell wall extracts (nonviable propionibacterium acnes/EqStim; NeogenVet EqStim), and autologous injection, have all been used to stimulate the immune system to respond to and eradicate sarcoids.⁴ Intravenous, intramuscular, and intratumoral injections have all been investigated. Intratumoral injection performed along with other treatments has some of the best described immunotherapy success rates.^2,5 Anaphylactic shock following injection is rare but has been reported.⁶ Although autologous vaccines have also found good rates of success, growth of the tumor at injection sites has been described and should be taken into consideration.

Radiation/brachytherapy

Radiation or brachytherapy typically caries the highest cost to owners and therefore is less common in practice. However, it remains the most powerful tool for treatment of sarcoid and should be considered in all cases of aggressive tumors or those in challenging or concerning locations.

Takeaways

Overall, sarcoid treatment remains challenging but a wide range of tools exist. Tumors that regrow following treatment are known to be more aggressive and challenging to defeat, and a more aggressive form of treatment should always be recommended.

A variety of treatment options can be successful, but failure of any treatment method can result in recurrence of a more aggressive tumor. Although this does not mean that aggressive treatment must be pursued in every case, owners should be informed of this risk when sarcoids are discovered or a treatment option is being pursued.

Elizabeth Collar, DVM, PhD, DACVS-LA, is an equine surgeon at the University of Tennessee, College of Veterinary Medicine, in Knoxville. She loves all aspects of equine surgery but has a particular interest in minimally invasive surgery and fracture repair. Her primary research interests include equine and translational musculoskeletal injuries and treatments. Collar enjoys teaching veterinary and equine surgical topics as well as equine musculoskeletal and lameness topics.

References

1. Offer KS, Dixon CE, Sutton DGM. Treatment of equine sarcoids: a systematic review. Equine Vet J. Published online March 14, 2023. doi:10.1111/evj.13935
2. Haspeslagh M, Vlaminck LEM, Martens AM. Treatment of sarcoids in equids: 230 cases (2008-2013). J Am Vet Med Assoc. 2016;249(3):311-318. doi:10.2460/javma.249.3.311
3. Knottenbelt DC, Patterson-Kane JC, Snalune KL. Sarcoids. In: Knottenbelt DC, Patterson-Kane JC, Snalune KL, eds. Clinical Equine Oncology. Elsevier; 2015:203-219.
4. Carr EA. Skin conditions amenable to surgery. In: Auer JA, Stick JA, Kümmerle JM, Prange T, eds: Equine Surgery. 5th ed. Elsevier; 2019:425-439.
5. Knottenbelt DC, Kelly DF. The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974 to 1999. Vet Ophthalmol. 2000;3(2-3):169-191. doi:10.1046/j.1463-5224.2000.00119.x
6. Vanselow BA, Abetz I, Jackson AR. BCG emulsion immunotherapy of equine sarcoid. Equine Vet J. 1988;20(6):444-447. doi:10.1111/j.2042-3306.1988.tb01571.x