Veterinarians have attacked sarcoids with everything from scalpels to lasers, and cryotherapy to caustic chemicals. But chemotherapy administered intratumorally could be a viable new option in removing and preventing future outbreaks, according to Alain Théon, DVM, MS, of the University of California, Davis., who presented at the 2006 AAEP Convention.

Théon reported this method prevented sarcoid recurrence in 97% of the 378 horses treated with it from 1996 through 2004. Théon injected cisplatin, a chemotherapy drug, directly into the tumor. He said this route maximizes the dose within the tumor, eliminating systemic exposure and toxicity.

Théon injected cisplatin (mixed with water and sesame oil to form a viscous gel) into the tumor while the horse was under heavy sedation. The outpatient procedure was repeated, with a total of four treatments given at two-week intervals for most patients. Théon reported the horses have tolerated this regimen well.

The intratumoral injection can also be used concurrently with surgery. Théon advised veterinarians to treat the entire area at risk with cisplatin, not just the tumor itself. In cases in which he removed the tumor, Théon treated the tumor bed and remaining affected surrounding tissues.

“You have to treat as wide as you would cut, if you were to do surgery (alone),” Théon said. Théon described one case in which he put sutures in the area surrounding the tumor to give himself a guide to the affected margin following its removal. Théon also advocated taking detailed photographs at each treatment to ensure the same total area received the drug. It’s very important to document what you’re doing because you want to treat the same volume of tissue time after time.”

Overall, the cure rate (sarcoid removal with no recurrence) using cisplatin alone was 93%. Cisplatin used concurrently with surgical removal prevented recurrence in 97% of cases. In tumors up to 10cm in diameter, the control rate was 92% up to three years following treatment. Of the 378 horses treated, 18 had tumors recur.

Théon showed photographs from horses before and following their cisplatin treatment. In almost all cases, the hair grew back in the treatment area and maintained its original color. “The cosmetic result is very good,” Théon said.

Known side effects of treatment include tenderness in the treated area and some edema (fluid swelling). Théon said other disadvantages of the treatment include the potential health risk cisplatin poses to humans, as it is a known carcinogen. Théon strongly advocated the use of full chemotherapy precautions in handling, mixing, and treating horses with the drug. He also suggested that practitioners not familiar with chemotherapy precautions meet with a human oncologist prior to using cisplatin on horses. The horse’s owner is also required to wear gloves when handling the horse for three days following treatment.

Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse’s AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads