Photodynamic therapy

Photodynamic therapy (PDT) is a type of cancer treatment based on the premise that single-celled organisms, if first treated with certain photosensitive drugs, will die when exposed to light at a particular frequency. PDT destroys cancerous cells by using this fixed frequency light to activate photosensitizing drugs which have accumulated in body tissues.

In PDT, a photosensitizing drug is administered intravenously. Within a specific time frame (usually a matter of days), the drug selectively concentrates in diseased cells, while rapidly being eliminated from normal cells. The treated cancer cells are then exposed to a laser light chosen for its ability to activate the photosensitizing agent. This laser light is delivered to the cancer site, (in the case of mesothelioma, the pleura), through a fiberoptic device that allows the laser light to be manipulated by the physician. As the agent in the treated cells absorbs the light, an active form of oxygen destroys the surrounding cancer cells. The light exposure must be carefully timed, so that it occurs when most of the photosensitizing drug has left the healthy cells, but is still present in cancerous ones.

The major side effect of PDT is skin sensitivity. Patients undergoing this type of therapy are usually advised to avoid direct and even indirect sunlight for at least six weeks. Other side effects may include nausea, vomiting, a metallic taste in the mouth, and eye sensitivity to light. These symptoms may sometimes come as a result of the injection of the photosensitizing agent.