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Photodynamic therapy (PDT) is a treatment that uses special drugs, sometimes called photosensitizing agents, along with light to kill cancer cells. The drugs only work after they have been activated or “turned on” by certain kinds of light. PDT may also be called photoradiation therapy, phototherapy, or photochemotherapy.
Depending on the part of the body being treated, the photosensitizing agent is either put into the bloodstream through a vein or put on the skin. Over a certain amount of time the drug is absorbed by the cancer cells. Then light is applied to the area to be treated. The light causes the drug to react and form a special kind of oxygen molecule that kills the cells. PDT might also help by destroying the blood vessels that feed the cancer cells and by alerting the immune system to attack the cancer.
The period of time between when the drug is given and when the light is applied is called the drug-to-light interval. It can be anywhere from a couple of hours to a couple of days, depending on the drug used.
The light used in PDT comes from certain kinds of lasers or from light-emitting diodes (LEDs). The kind of light used depends on the type of cancer and where it is located in the body. PDT is usually done as an outpatient procedure (meaning you won't have to stay in the hospital) but is sometimes combined with surgery, chemotherapy or other anti-cancer drugs, or radiation therapy.
But PDT has limits, too:
PDT can be used in people with certain types of cancer to help them live longer and improve their quality of life. It’s becoming more widely recognized as a valuable treatment option for certain types of localized cancers (cancers that have not spread far from where they started).
Several photosensitizing agents are currently approved by the US Food and Drug Administration (FDA) to treat certain cancers or pre-cancers. Here are two of the most widely used:
Researchers are always looking for new PDT drugs, and new ways to give them. PDT is also being combined with other types of treatment, such as surgery and radiation therapy. Future possibilities include other combination treatments with PDT drugs, as well as new PDT drugs that can target tumor cells better, can leave normal cells more quickly, and allow the treatment light to penetrate deeper.
Not everyone getting photodynamic therapy will have the same side effects. Be sure to ask your doctor which side effects you might expect, what can be done to help, if there are any treatments for your side effects, and which side effects you need to report right away. Get the phone number to call if you have problems after regular office hours.
The most common side effect of PDT is sensitivity to bright lights and sunlight. These reactions caused by PDT light can show up on the skin where the drug is applied. They usually involve redness and a tingling or burning sensation. For a period of time after treatment, you'll need to be careful to not expose treated areas of your face and scalp to light.
Sunscreens will not protect the skin from photosensitivity reactions.
Depending on the type and location of treatment, the treated skin might turn red and may swell for a period of time. With some treatments, blisters may form. This may last hours to days after treatment. The skin may also have a burning sensation or may be itchy or change color after treatment.
Swelling in the treated area can lead to pain and problems with the tissues and organs working properly.
Sometimes PDT treatments can make the immune system work differently, usually by stimulating it to work more. Sometimes it can become weaker for period of time. In very rare cases, PDT can cause skin cancer at the site where treatment was given. Some researchers believe this happens if the immune system is weakened by PDT.
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Last Revised: November 19, 2021