Photodynamic therapy (PDT) is a treatment that uses a drug called a photosensitizer with a specific type of light to kill cancer cells. There are different types of photosensitizers, some of which are injected intravenously and some of which are applied topically. The agent is absorbed by normal cells as well as cancer cells, but stays in cancer cells longer. The tumor is exposed to light after a period of time (30 minutes up to 72 hours) once the photosensitizer has left normal cells. The photosensitizer in the tumor absorbs the light and produces an active form of oxygen that destroys the tumor cells. PDT not only can directly kill tumor cells, but can shrink or destroy tumors by damaging intratumoral blood vessels and by activating the immune system.
The light needed to activate most photosensitizers is unable to pass through tissue thicker than 1 cm. For this reason, PDT is usually used to treat tumors of the skin or on the lining of internal organ or cavities. PDT is less effective on large tumors, because the light cannot pass very far into the mass. PDT is used for localized tumors and cannot be used to treat metastatic cancer.
PDT is generally performed as an outpatient procedure and may be used in combination with other therapies such as radiation, surgery, and chemotherapy. Because the photosensitizers tend to build up in tumors and the activating light is focused on the tumor, damage to healthy tissue is minimal.
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