Despite the numerous treatment choices available for equine sarcoids, no modality is 100% effective in producing a cure. So which of the numerous treatment options should veterinarians use to treat this common equine tumor? The answer depends on a number of factors, and at the 2012 Western Veterinary Conference, held Feb. 19-23 in Las Vegas, Nev., one researcher gave a rundown of evidence-based sarcoid treatment options.
Small sarcoids generally cause little disruption in a horse's daily life. Under certain circumstances, however, these tumors can spontaneously grow into a nuisance, a health risk, and an eyesore. In such cases, "early recognition coupled with appropriate treatment is paramount to a successful outcome," explained Ann Rashmir-Raven, DVM, MS, Dipl. ACVS, associate professor of Large Animal Clinical Sciences at Michigan State University's College of Veterinary Medicine.
"The treatment modality selected is determined by many variables, including sarcoid tumor type and location, aggressiveness of the tumor, clinical experience, client compliance, treatment costs, patient behavior, and the availability of services, equipment, and facilities," she added. In short, it's not an easy decision.
She noted that regardless of the option selected, treatment must be aggressive. Rashmir-Raven reviewed some common evidence-based treatment options:
Surgical Removal--While this is a relatively easy procedure to carry out in most cases, Rashmir-Raven noted it has a recurrence rate of 15 to 82%, with the majority of tumors growing back more aggressively and within six months. "Surgical excision is better used to reduce tumor volume and improve killing efficiency of other treatment modalities," she suggested. She gave practitioners in attendance some tips on removing sarcoids, but stressed using adjunctive treatment options.
Laser Removal--The concept of laser removal isn't too different from surgical removal; however, it might offer some benefits over the latter option, Rashmir-Raven noted: "Because laser energy is absorbed by surrounding tissues, tumor cells are killed up to 0.2 mm beyond the wound margins." The downside? This method of excision has the potential to aerosolize infectious particles and agents from the sarcoid being removed, and Rashmir-Raven said it's unclear what impact this could have on the horse and/or surgeons performing the procedure. Like surgical removal, she suggested veterinarians use laser removal in conjunction with another treatment option.
Cryotherapy--Although cryotherapy is a cost-effective sarcoid treatment option, Rashmir-Raven noted, "recurrence rates vary widely for this procedure with some authors reporting little success (1%) and others reporting 100%." In this procedure veterinarians use liquid nitrogen to literally freeze the tumor off the horse's body. Rashmir-Raven noted that cryotherapy typically results in scarring and hair depigmentation at the site of removal, so this isn't the most cosmetic removal option. Additionally, she said, "due to the significant tissue destruction associated with cryotherapy, it might not be appropriate for tumors near the eye, nostrils, or similarly significant structures."
Intratumoral Hyperthermia--Intratumoral hyperthermia, in which the sarcoid is heated, has reportedly been successful in treating equine sarcoids, she said. "More recently hyperthermia treatments have also included concomitant (when multiple drugs are given at or almost at the same time) chemotherapy," Rashmir-Raven added. Unfortunately, hypertherapy units are not readily available in private practice.
Cisplatin Injections and Beads--One of Rashmir-Raven's choice treatments is the chemotherapeutic drug cisplatin, which is used in both injectable form and beads. She reported that cisplatin "consistently provides long-term control of equine sarcoids with a 96.4% resolution rate (3.7% recurrence rate) after four years in 409 cases."
When using a cisplatin injection, she explained that tumors are generally injected three to five times, every two to three weeks. Large sarcoids, she said, should be debulked prior to cisplatin treatment. When using cisplatin beads--which release the drug slowly over the course of 30 days--the practitioner inserts the beads in the tumor and the surrounding areas, she explained. Rashmir-Raven said she prefers the beads to the injection for most sarcoids due to the ease of placement.
"Long-term results with cisplatin ... have provided the best tumor resolution rate of all the published sarcoid treatment modalities," Rashmir-Raven said.
She briefly discussed the use of cisplatin electrochemotherapy in treating sarcoids, noting that one clinical trial that yielded a 99.5% success rate. Horses require general anesthesia for electrochemotherapy, so treatment cost is typically high, she noted.
Topical Acyclovir--Rashmir-Raven explained the topical application of the antiviral drug acyclovir is considered a safe and cost-effective treatment and surgical excision. In one study she discussed, acyclovir reduced the size of all 47 treated sarcoids and completely resolved 68% of those tumors. "Acyclovir is proposed to be routinely used for the treatment of flat and mild-type sarcoids or potentially as a relatively economical way to shrink tumors prior to the use of cisplatin," she said. She added that the cream or ointment should be applied daily for two to six months.
Topical Immiquimod--Known by the trade name Aldara, Rashmir-Raven said that in studies immiquimod has reduced nondebulked tumor size by as much as 75%, and she added that her personal results with the drug have been even more effective when used on tumors that have been debulked. The drug is applied every other day for 32 weeks or until the tumor is resolved, she said. Potential side effects from immiquimod use include inflammation, oozing, hair depigmentation, and hair loss.
Topical Bloodroot Extract--Rashmir-Raven discussed the use of a bloodroot extract salve used to treat a variety of skin conditions, including sarcoids. She relayed that the salve, marketed under the trade name Xxterra, is an economical option for some small sarcoids and larger sarcoids for which more expensive treatment isn't an option. Sarcoids typically begin sloughing in seven to 10 days, and treatment is often required more than once.
Bacillus Calmette-Guerin (BCG) Injection--Rashmir-Raven explained that BCG injections--one type of sarcoid "immunostimulant"--are known to have good success rates in treating sarcoids around the eyes (83-100% efficacy); however, the success rates drop to less than 50% when treating sarcoids located elsewhere on the body. Additionally, she said, severe inflammatory and allergic reactions and anaphylaxis (a rapidly developing and sometimes life-threatening allergic reaction) have been known to occur when using BCG.
Autogenous Vaccines and Sarcoid Implantation--Essentially autogenous vaccines are created using tissue from the patient's own body to prompt an immune response, Rashmir-Raven explained. "Similarly, the removal, freezing, and reimplantation of a sarcoid into the same horse has demonstrated success in a limited number of cases," she added. Also, while tumor implantation using sarcoids from a different horse has decreased the size of some sarcoids, it has also been known to stimulate the growth of new tumors, she reminded. "Because other less-invasive treatments frequently work well and tumor transplantation from a donor horse bears risks--such as tumor production and transmission of other diseases--this procedure should be reserved for refractory cases," Rashmir-Raven stressed.
Although science and research on sarcoid treatments has advanced and produced some viable therapy modalities, there's no one option that will cure all sarcoids. Work with a veterinarian to determine which treatment option is best in each particular case.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.