Photodynamic Therapy (PDT)

What is Photodynamic therapy (PDT)?

Photodynamic therapy (PDT) is a treatment that uses light to damage cancer cells or abnormal tissue. For PDT, there must be a light source (such as a laser) combined with a drug (called a "photosensitizer”) that makes the tissues sensitive to light. Cancer cells are affected by photosensitizers more than normal cells are.

How does PDT work?

When a certain wavelength of light and a photosensitizer drug are combined, a form of oxygen is made. This form of oxygen is called an oxygen free radical. These oxygen free radicals kill cancer cells.

Depending on the area of the body to be treated, there are different photosensitizing drugs and different wavelengths of light that can be used. Over a certain amount of time (depending on the photosensitizer you were given), it gets absorbed by cells all over the body, staying in cancer cells longer than normal cells. The wavelength controls how far the light can travel into your body. PDT is not often used to treat large tumors because the light cannot go deep enough to treat those tumors.

There are a few ways that PDT can kill cancer cells:

• Direct damage to cells caused by oxygen free radicals.
• There are also indirect effects.  There can be damage to blood vessels that give blood to the tumor, both during the treatment and after the treatment is over. This deprives tumor cells of oxygen and nutrients they need, causing cell death.
• A new type of PDT is being studied, called photoimmunotherapy (PIT). In PIT, an immune protein delivers the photosynthesizer to cancer cells. PIT stimulates (revs up) your immune system to attack the cancer cells.

What does PDT treat?

PDT may be used to treat: 

• Obstruction (blockage) caused by esophageal cancer or non-small-cell lung cancer (NSCLC). 
• Lung cancer when surgery or radiation cannot be used. 
• Barrett's Esophagus (when the cells that line your esophagus turn to cells that aren’t normally in your esophagus) and high-grade dysplasia (cells look very abnormal under a microscope).
• Actinic keratosis (scaly, rough patches of skin caused by sun exposure).
• Basal cell and squamous cell skin cancer.
• Cutaneous T-cell lymphoma.
• Age-related macular degeneration (eye disease that can cause vision loss).

What can I expect during PDT?

PDT is often done as an outpatient procedure, depending on the site that is to be treated. Your provider will give you specific details, but in general:

• A few hours to up to a day before your PDT, you will be given a photosensitizer medication. This is given by mouth, intravenously (IV, into a vein), or topically (on the skin).
• Your provider then points the light at the area of the cancer. The photosensitizer is activated, and the cancer cells are destroyed. Since the photosensitizing drug stays in cancer cells longer, the cancer are damaged more than the healthy cells that have already cleared the drug.

PDT may be repeated and may be done with other treatments, such as surgery, radiation, or chemotherapy.

What are the side effects of PDT?

Photosensitizers make your body sensitive to light. Your provider will tell you how long you should avoid light exposure. You will be given light precautions, such as avoiding direct sunlight and bright indoor light for a period of time.

If light precautions are not followed, you could have burns, swelling, and pain. Other side effects of PDT are related to the area that is treated and may be coughing, trouble swallowing, stomach pain, painful breathing, swelling, and/or shortness of breath. If you have trouble breathing, call 911 or go to the nearest emergency room.