A medication used to treat external tumors in humans has shown some promise of treating sarcoids in horses. In a University of Minnesota (UM) pilot study, researchers used imiquimod (Aldara) to treat horses with mixed, fibroblastic, flat, verrucous, and nodular type tumors. Horses were treated three times weekly with imiquimod by the owners for 32 weeks, or until the tumor was resolved (which ever came first). The study was published in the Aug. 17 issue of Veterinary Dermatology.

Sarcoids are the most common equine tumor. Although they are not malignant, they can be very difficult to control. According to Erin Malone, DVM, Dipl. ACVS, PhD, associate clinical specialist at UM, treatment with imiquimod can lead to a local inflammatory response, which triggers an immune response. Imiquimod is a topical medication that acts as an immune response modifier, and it has been shown to have potent antitumor and antiviral effects.

The study’s results showed imiquimod to be 75% effective in reducing sarcoids, and 60% effective in totally resolving them.

Common side effects of imiquimod treatment included redness, swelling, oozing, crusts, and pain on palpation; however these are normally localized to the area of application.

According to Malone, the cost to treat a small tumor is approximately $100 per month, which is comparable to most other sarcoid treatments. For more information on the use of imiquimod as a sarcoid treatment see www.cvm.umn.edu/cic/completedstudies/lamedsurg/aldarardvm.html