SIDEBAR: Photodynamic Therapy for Cancer

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Photodynamic therapy is a two-step treatment that includes a photosensitizing agent and a light source. In the first step, the photosensitizing agent (porfimer sodium) is injected into the bloodstream and absorbed by all cells. Over 24 to 48 hours, the drug is concentrated in cancer cells. In the second step, tumor is eliminated with a laser at 630 nm; the site of treatment dictates the length of exposure, which can be 8 to 12 minutes in the airway.

The light activates the photosensitizing agent, producing an active form of oxygen, which destroys nearby cancer cells. The light is directed through thin fiber optic cables. These fiber optic cables are then passed through an endoscope for esophageal tumors or a bronchoscope for lung tumors. For surface tumors such as skin cancer, other light sources may include light-emitting diodes. Not only does photodynamic therapy directly kill cancer cells, it also seems to damage the blood vessels in the tumor and may activate an immune reaction to attack the tumor cells.

Drawbacks and Advantages

The one noted side effect of photodynamic therapy is photosensitivity, which may last for at least 30 days after treatment. After undergoing photodynamic therapy, it is necessary to avoid bright indoor lights and direct sunlight. Sunscreen is not protective in this case, as the photosensitivity is caused by visible light, not ultraviolet light. Some indoor light is good, however, to help break down the drug in the skin. Although photosensitivity is a concern after photodynamic therapy, with the proper precautions, nursing assistance, and patient education, it is a manageable, temporary side effect.

Generally, photodynamic therapy is performed as an outpatient procedure and can be repeated. Photodynamic therapy can be used alone or in conjunction with other cancer treatments, such as surgery, radiotherapy, or chemotherapy. Ongoing studies with photodynamic therapy are focusing on how best to employ this technology as well as ways to improve its effectiveness; one promising option is to join the photosensitizing agent with a targeted chemotherapy drug. Research continues to center on refining the photosensitizing agents for a more powerful, tumor-specific result; developing light sources that can penetrate tissue and treat deeper tumors; and improving equipment and light delivery. ■

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International Photodynamic Medicine Symposium: Shedding New Light on an Old Therapy

This past May, a collaborative think tank of researchers was convened at The Ohio State University, Columbus, to share their expertise in a somewhat older treatment that is reemerging on many fronts: photodynamic therapy.

Participants from the United States, Great Britain, and Japan took part in...