STANFORD, Calif., Feb. 17 -- Researchers at Stanford University Medical Center announced plans to test laser-based photodynamic therapy (PDT) as a new way to help cancer patients to breath. According to Richard I. Whyte, chief of Stanford University's Division of Thoracic Surgery, select patients whose breathing has been impaired by lung or esophageal cancer will be eligible for the treatment. Whyte said that PDT holds promise for treating a variety of cancers, pending further research.In PDT, patients are injected with a light-activated drug that is selectively retained by malignant cells, which are then exposed to light from an excimer laser delivered via a fiber-optic probe threaded into the esophagus or bronchial tubes. Exposure triggers a photochemical reaction in the drug-laden malignant cells, destroying the cancerous cells and leaving normal cells unharmed.Whyte said prime candidates for PDT include individuals too frail for surgery, patients with cancer too advanced for traditional tumor removal, and those with tumors that continue to grow unchecked despite surgery. Overall, PDT shows benefits for 80 percent of patients appropriately selected to receive the procedure, Whyte explained. Although the treatment typically is not a cure, it helps patients by shrinking tumors to reduce pain, improve swallowing and allow breathing to continue normally.