Less Drug, Stronger Laser Beam Allow Photodynamic Therapy To Reach Deep Chest Cancer Lesions, UB Researchers Find

RENO, NEV. -- Photodynamic therapy (PDT), one of the most promising new cancer treatments, may have much wider application than previously thought, new research by University at Buffalo researchers has shown.

Thomas S. Mang, Ph.D., UB clinical associate professor of oral and maxillofacial surgery, has found that by manipulating the amount of a light-sensitive drug and the intensity of the laser beam that activates it, he can successfully treat cancer cells deeply embedded in the chest wall without damaging surrounding normal tissue.

This low-dose PDT approach has resulted in complete healing in nearly 90 percent of 102 recurrent breast-cancer lesions.

Mang will present his findings here on April 8 at the annual meeting of the American Society for Laser Medicine and Surgery.

"These results offer further proof of the ability to lower drug concentrations and raise light intensity to successfully treat certain difficult tumors," said Mang, who conducted the study at the Photodynamic Therapy Center in Buffalo General Hospital of Kaleida Health, which he directs. "It allows broader application of this therapy in patients who can truly benefit from it."

PDT was developed at Roswell Park Cancer Institute, the site of UB's basic cancer research programs, and is thought to have significant potential for treating certain types of cancers. It has been approved to date for general use in treating non-small-cell lung cancer and obstructing esophageal tumors, and is being used on an experimental basis for several other tumor types.

The procedure exploits the propensity of cancer cells to absorb higher than normal concentrations of photosensitive drugs. When exposed to light via lasers, these drugs become toxic and destroy the malignant tissue. Since normal tissue surrounding tumors also absorbs a certain amount of the drug, the goal of researchers and clinicians is to find a drug-to-light ratio for each tumor type that will kill the most tumor cells while sparing the most normal tissue.

In the current study involving breast-cancer lesions that had formed on the chest wall, Mang lowered the standard 2.0 mg/kg dose of Photofrin, a photosensitive drug, to 0.8 mg/kg. "If we used the standard drug dose, we never would have been able to use a light dose that would reach deep enough to kill the tumor cells without destroying normal tissue," he said.

"By lowering the drug dose, the small amount of the drug in normal tissue bleaches out before it does any damage, and by delivering more light, we can reach deeper into tumors where the drug concentration is still high enough to kill cancer cells."

Mang and Ronald R. Allison, M.D., UB associate professor of clinical radiation oncology, treated nine patients with a total of 102 chest wall lesions. All the women had undergone surgery, full dose radiation and multiagent chemotherapy.

After receiving PDT, 89 percent of the lesions healed completely without scarring, Mang found. Of the remaining lesions, 8 percent became smaller. Three percent did not respond to the treatment.

"These results offer a glimpse of the parameters one might be able to use for treating whole fields of disease with little normal tissue damage," Mang said. "It gives us very good local control of disease."