The short answer
Photodynamic therapy uses a drug activated by light, called a photosensitizer, to kill cancer cells. It is a two-step, local treatment used for certain skin, esophageal, and lung cancers and some precancers. It limits damage to healthy cells but only reaches tumors on or just below the surface.
Photodynamic therapy (PDT) uses a light-activated drug called a photosensitizer to kill cancer cells.
It is a two-step process: first the drug is given, then the tumor is exposed to light.
It is a local treatment used for certain skin, esophageal, and lung cancers and some precancers.
It limits damage to healthy cells and does not cause scarring.
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The full explanation.
The simple version
Photodynamic therapy uses a drug that is activated by light, called a photosensitizer, to kill cancer cells. The light can come from a laser or another source, such as LEDs. It is most often used as a local treatment, which means it treats a specific part of the body. It is also called PDT.
PDT uses a light-activated drug to destroy cancer cells in a specific spot.
How it treats cancer
When cells that have absorbed the photosensitizer are exposed to a specific wavelength of light, the drug produces a form of oxygen, called an oxygen radical, that kills them.
Photodynamic therapy may also damage blood vessels in the tumor, which keeps it from getting the blood it needs to grow. And it may trigger the immune system to attack tumor cells, even in other areas of the body.
The two steps
Photodynamic therapy is a two-step process:
- First, you receive the photosensitizer. The drug may be taken by mouth, spread on the skin, or given through an IV, depending on where the tumor is. After 24 to 72 hours, most of the drug has left normal cells but remains in cancer or precancer cells.
- Then the tumor is exposed to the light source. How the light is applied depends on where the tumor is. For skin tumors, the light is aimed right at the cancer. For tumors in the throat, airways, and lungs, the doctor inserts an endoscope — a thin, lighted tube — down your throat, then threads a fiber optic cable through it to deliver light to the treatment area.
Most often, PDT is done as an outpatient, so you go home the same day. It may be given by itself or with other cancer treatments.
One type of PDT, called extracorporeal photopheresis (ECP), treats abnormal white blood cells in people with cutaneous T-cell lymphoma. A machine collects your blood cells, treats them with a photosensitizer, exposes them to light, and returns them to your body.
What it treats
The FDA has approved photodynamic therapy to treat:
- actinic keratosis
- advanced cutaneous T-cell lymphoma
- Barrett esophagus
- basal cell skin cancer
- esophageal (throat) cancer
- non-small cell lung cancer
- squamous cell skin cancer (stage 0)
PDT is also used to relieve symptoms of some cancers, such as esophageal cancer when it blocks the throat and non-small cell lung cancer when it blocks the airways.
Benefits and drawbacks
Benefits. PDT limits damage to healthy cells, because the photosensitizer tends to build up in abnormal cells and the light is focused directly on them. It also does not cause scarring, which makes it a good option for people with skin cancers and precancers.
Drawbacks. PDT can still harm normal cells in the treatment area and cause side effects. The light cannot pass through more than about a third of an inch (1 centimeter) of tissue. So PDT can only be used for tumors that are on or just under the skin, or on the lining of internal organs or cavities. Because the light cannot reach far into large tumors, it is less helpful for them.
Side effects
Damage to normal cells is limited, but PDT can still cause burns, swelling, pain, and scarring in the treatment area. Other side effects depend on the area treated and can include cough, trouble swallowing, stomach pain, painful breathing, shortness of breath, and skin problems such as redness, stinging, swelling, or itching.
One type of photosensitizer makes the skin and eyes sensitive to light for about 6 weeks. During this time, you should avoid direct sunlight and bright indoor light. ECP can cause brief low blood pressure, a faster heart rate, anemia, and a low platelet count. Side effects improve once treatment is over.
Because one photosensitizer leaves skin and eyes light-sensitive for weeks, follow your team's advice on avoiding bright light.
Words to know
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Common questions
▸What is photodynamic therapy?
Photodynamic therapy uses a drug that is activated by light, called a photosensitizer, to kill cancer cells. The light can come from a laser or another source, such as LEDs. It is most often used as a local treatment, meaning it treats a specific part of the body. It is also called PDT.
▸How does photodynamic therapy work?
When cells that have absorbed the photosensitizer are exposed to a specific wavelength of light, the drug produces a form of oxygen that kills them. PDT may also damage blood vessels in the tumor and can trigger the immune system to attack tumor cells.
▸How is it given?
It is a two-step process. First you receive the photosensitizer by mouth, on the skin, or through an IV. After 24 to 72 hours, most of the drug has left normal cells but remains in cancer cells. Then the tumor is exposed to the light source. For deeper tumors, an endoscope may be used to bring the light inside the body.
▸What cancers does it treat?
The FDA has approved PDT to treat actinic keratosis, advanced cutaneous T-cell lymphoma, Barrett esophagus, basal cell skin cancer, esophageal cancer, non-small cell lung cancer, and stage 0 squamous cell skin cancer. It is also used to relieve symptoms of some esophageal and lung cancers that block passages.
▸What are the benefits of PDT?
PDT limits damage to healthy cells because the photosensitizer builds up in abnormal cells and the light is focused on them. It also does not cause scarring, which makes it a good option for people with skin cancers and precancers.
▸What are the drawbacks and side effects?
The light cannot pass more than about a third of an inch (1 centimeter) into tissue, so PDT is only used for tumors on or just under the skin or the lining of organs. Side effects can include burns, swelling, pain, and scarring in the treated area, and one photosensitizer makes the skin and eyes sensitive to light for about 6 weeks.
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