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DURHAM, N.C. - Physicians at Duke University Medical Center have started using laser light to activate a drug that destroys tumors blocking the airways.

This treatment, called photodynamic therapy, is available for lung cancer patients at only a few medical centers, according to Dr. Tom D'Amico, a surgeon in Duke Comprehensive Cancer Center. Duke is the only center in North Carolina using this technology regularly to treat lung cancer patients, and one of only two in the Southeast. The other is at the University of Alabama.

"This is not a clinical trial, this is an approved treatment," explains D'Amico. "It might offer an option for those patients who can't be treated with traditional surgery, and it might even be a better option for some who can."

In photodynamic therapy, cancer cells accumulate a special drug that is activated by light. Once turned on, the drug creates oxygen radicals - highly reactive oxygen atoms that damage DNA - and the cells die. The light can penetrate a certain thickness depending on the power used, so the therapy can completely clear obstructed airways. The dead cells are either removed through a bronchoscope or by coughing.

The treatment provides a very tangible improvement in patients' quality of life, according to D'Amico. If tumors block the airways - the trachea leading to the lungs or the bronchi that let inhaled air fill the lungs - breathing can be labored to the point of severely limiting activities or requiring supplemental oxygen. By clearing these airways, D'Amico lets these patients breathe easily again.

In early stage lung cancer patients, research studies, primarily from Europe and Japan, demonstrate longer survival and up to twice as many complete remissions with PDT compared to other treatments. While some studies had better results for patients with tumors less than 1 cm long, new laser probes are being designed to let physicians treat a wider variety of patients, D'Amico says.

Photodynamic therapy is also used at Duke to destroy tumors that block the esophagus in esophageal cancer. In clinical trials comparing heat-inducing laser surgery to photodynamic therapy for esophageal cancer, the two methods had similar capabilities to destroy tumor and improve survival. The photodynamic therapy treatment, however, was able to treat a wider range of tumor shapes and was less likely to rupture the esophagus. Photodynamic therapy was also better-tolerated by patients than the laser surgery.

Until now, laser surgery has been the primary option for clearing the trachea when it is obstructed by a tumor. But this can take hours of carefully burning tumor tissue with a heat-producing laser, D'Amico says. By contrast, photodynamic therapy takes only eight to nine minutes to activate the drug with light.

"Using a heat-producing laser is not only more time intensive, it's also more dangerous," D'Amico says. "With photodynamic therapy it's easier to control the depth of tumor treated, reducing the risk of a possibly deadly rupture."

The treatment has two steps. First, the drug Photofrin, which makes cells become extremely sensitive to light, is given to patients and allowed to circulate through the body. After two days, the cancer cells have accumulated the drug and, using an endoscope, the physician shines a non-thermal laser through optic fibers onto the tumor. A predetermined dose of light then activates the drug, killing the tumor cells.

A side effect of the treatment is that the drug also accumulates in skin cells. As a result, patients must avoid exposure to bright light for about four weeks because extreme burns can result from the skin's increased sensitivity.

D'Amico emphasizes that PDT is unlike any other treatment - it can be repeated any time the tumor begins to grow back. Radiation therapy, on the other hand, is limited by the radiation dose the rest of the body gets - particularly other organs near the tumor, like the heart - and chemotherapy can be limited by its unavoidable damage to some normal tissues. PDT also preserves the lung. Traditional surgery removes normal tissue and tumor tissue, and treatment with radiation hurts lung tissue in the path of the beam.

PDT, however, does have its limitations. Right now, only tumors that can be reached by the fiberoptic laser can be treated with PDT, says D'Amico, although research is continuing to expand its uses. The University of Pittsburgh Medical Center treats the most lung cancer patients with photodynamic therapy. Other centers in the East that regularly use photodynamic therapy to treat lung cancer patients include the University of Alabama, Brigham and Women's Hospital in Boston, and the University of Pennsylvania, according to D'Amico, who was trained by physicians at the University of Pittsburgh.

The first two patients with tumors obstructing the airways were treated with the process at Duke on March 30. A dozen more patients have since been treated and new patients are being scheduled.

Photodynamic therapy was approved by the FDA in January 1998 to treat early stage lung cancer patients. FDA approval was granted in late 1998 to extend the treatment to ease symptoms in patients with airway-obstructing tumors in advanced lung cancer. Japan, Canada and several European countries approved PDT for various uses prior to approval in the United States.