Sarcoids are the most common equine tumors, said Youssef Tamzali, DVM, PhD, of the Ecole Nationale Veterinaire (National Veterinary School) in Toulouse, France, during his presentation at the 2003 American Association of Equine Practitioners' convention on Nov. 25. One of the most common and effective treatments for sarcoids is chemotherapy using the drug cisplatin, which is noted for its ease of use, low cost, and high efficacy (up to 90% for sarcoids and 70-90% for carcinomas). However, its use is limited to small tumors under five centimeters in diameter, Tamzali said. In addition, repeated cisplatin treatments must be done over a period of time.

Preliminary results from a study done by Tamzali and associates has found that electrochemotherapy (ECT) can enhance the effectiveness of cisplatin. The main disadvantage of cisplatin is poor diffusion (spreading) of the drug into the tumor cells. This is why it is mixed with sesame oil in order to prolong its time at the tumor site. In previous laboratory studies using electropermeabilization (use of an electric pulse) of cells, the concentration of cisplatin in cells has been increased 100 fold.

Tamzali explained that if you first administer a drug, it will surround the cell, but if electrical pulses are applied, the drug enters the permeabilized cells, resulting in a fast and significant increase of drug concentration and an expected increase in antimitotic effect (anti-cell division). With this in mind, Tamzali set out to determine the effect on horses.

From October 1999 to June 2003, tumors were treated in 30 horses. Treatment consisted of an injection of cisplatin into the tumor and surrounding tissues. Five minutes afterward, the horses underwent electrical treatment through electrodes brought into contact with the skin. General anesthesia was used over local anesthesia since horses tended to panic as a result of the electric pulses under local anesthesia. All horses underwent successive treatments after two weeks, with no more than four treatments. The horses were monitored for a period of two years