Photodynamic therapy (PDT) is a cancer treatment that uses a drug and a certain type of laser light to kill cancer cells. A drug that is not active until it is exposed to the light is injected into a vein. The drug is picked up preferentially by the cancer cells, as opposed to normal cells.
Fiberoptic tubes are then used to carry the laser light to the cancer cells. Exposure of the drug to light starts a chemical reaction that produces substances that are toxic to the cells, thereby killing them off. Because the tumor cells absorb more of the drug than normal cells, the tumor cells are preferentially killed; thus PDT causes little damage to healthy tissue. PDT is currently approved for use in Canada, but is still considered investigational for the treatment of bladder cancer in the United States. PDT is approved in the United States for other cancers, including esophageal and lung cancer.