Photodynamic Therapy (definition of)

Photodynamic therapy (PDT) uses a specially-designed light-sensitive drug known as a photosensitizer, enabling oncologists to use light in order to kill cancer cells. When the drug is administered and exposed to a specific wavelength of light, it produces a form of oxygen that kills cancer cells.

After the photosensitizing agent is injected into the bloodstream, it is absorbed by cells throughout the body. However, malignant cells absorb significantly more of the drug that healthy, normal ones; within three days, most of this agent has been metabolized by normal cells while remaining in malignant ones. The tumor is then exposed to light, either from light-emitting diodes (LEDs) that are applied to the skin's surface (in the case of melanoma) or from a laser that is directed down an endoscope that is inserted into the patient's body. The photosensitizer then absorbs the light, destroying the cancer cells while sparing normal tissues.

PDT is generally an outpatient procedure that may involve multiple treatments. If may also be adjuvant to more conventional cancer therapies. Currently, the use of PDT is generally limited to tumors that on the skin or in areas that are no more than one-third inch below the surface. The FDA has approved the use of PDT for some lung cancers as well as that of the esophagus. PDT is at present being studied as a possible treatment for mesothelioma