CORVALLIS - A "photodynamic therapy" for the treatment of certain types of cancers shows considerable promise in treating horses, and new research that is under way at the College of Veterinary Medicine at Oregon State University may eventually expand use of this therapy in humans.

A research project at OSU is successfully using the glowing lights of this therapy to treat horses that have certain kinds of viral-associated and frequently recurring sarcoid skin tumors. These are somewhat common in horses and usually not fatal, but can cause pain, bleeding, infection and disfigurement, leading to blindness or inability of the horse to perform physically.

But the studies, scientists say, may also have direct application to the expanded use of this therapy in human medicine. Its use in both humans and animals is still in the clinical trial and preliminary stages, but the therapy may have various advantages over some other types of conventional cancer therapies, and may also help stimulate an immune response better than some other approaches.

The therapy works by giving a human or animal a chemotherapeutic drug, either topically, by injection or intravenously. But the drug is not activated as a cancer-killing agent until a bright light shines upon it, either from a laser or light emitting diodes. This allows a very specific targeting of the chemotherapeutic drug, is less invasive, less disfiguring than surgery, and causes minimal or no systemic toxicity.

"There's no doubt the use of this procedure is showing promise in veterinary medicine and may have expanded use in the future," said Dr. Scott Gustafson, a veterinary surgeon at OSU. "With further research the treatment should become practical, useful and cost effective."

With humans, Gustafson said, photodynamic therapy is very new and being used primarily as a last option in treatment of certain types of lung, skin, breast or esophageal cancers. But evidence of its broader use and proven efficacy in horses may lead to wider possibilities being considered for humans, he said.

OSU veterinary doctors are already seeking funding from the National Institutes of Health for an extensive clinical trial, Gustafson said, and collaboration on this project is under way with the Oregon Medical Laser Center in Beaverton. Some of the current goals include determining the optimal drug dosage, light intensity, and duration of light treatment for photodynamic treatment of sarcoid lesions.

"Another possible advantage is that this type of therapy doesn't totally disrupt cancer cells, it just shuts down their biological function, resulting in programmed cell death," Gustafson said. "This could leave surface antigens in place that could help the body mount a better immune response to the cancer."

A horse just treated at OSU with this procedure had tumors on its ears that had been treated 11 different times without success, mostly with surgery. The existing treatments for horses with multiple sarcoid tumors have a very low success rate, Gustafson said.

Some other uses of this treatment for various tumors in cats and dogs have also been explored, veterinary experts say.

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Dr. Scott Gustafson, 541-737-6963