Photodynamic Therapy: Light-Based Cancer Treatment

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.

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.

Photodynamic therapy is a two-step process:

1. 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.
2. 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.

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. 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.

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.

• Call 911 or go to an emergency department if breathing becomes hard or noisy after treatment in the airway or food pipe, or you cannot swallow your own spit. Swelling in a treated airway can close it off.
• Phone your care team at once, day or night, if you run a temperature of 100.4°F (38°C) or higher while you are also receiving chemotherapy. CDC treats fever during chemotherapy as a medical emergency. If you cannot reach them quickly, go to an emergency department and say you are on chemotherapy.
• Call your care team the same day if the treated area blisters, weeps, or hurts more each hour. Do the same for a burning pain on breathing, or for a temperature of 100.4°F (38°C) or higher when PDT is your only treatment.
• Call your care team within a day or two if a light exposure has left your skin stinging and red, if swallowing stays sore enough to cut down what you eat, or if pain relief at home is no longer enough.

Source: NCI — Photodynamic Therapy to Treat Cancer. Fever threshold and urgency from CDC — Fever and Cancer Treatment.