Photodynamic therapy (PDT)

Photodynamic therapy (PDT) uses special medications combined with light to destroy cancer and precancer. This treatment is also called blue light therapy, red light therapy or phototherapy.

PDT may be used to treat many types of cancer. This article will review PDT, its uses, what to expect during light therapy and phototherapy side effects.

What is PDT treatment?

PDT works with chemicals that create toxic oxygen radicals when they’re hit with light. These special drugs are called photosensitizers or photosensitizing agents. When exposed to a photosensitizer, cancer cells absorb and hold on to the drug. When hit with light from a laser or light-emitting diode (LED), the oxygen radicals they make may destroy cancer cells.

PDT is a local treatment, which means that it’s only used on the body parts that contain cancer cells. This limits the damage to healthy cells.

Unlike radiation therapy, PDT may be used in the same area multiple times. It’s also less risky than cancer surgery, takes less time and costs less than many other cancer treatments.

Doctors use different types of PDT for different cancers. For example:

Blue light therapy uses the photosensitizer aminolevulinic acid (Levulan Kerastick^®). A doctor applies this drug to the skin and activates it with a special blue light. This may be used for conditions like actinic keratosis.

Red light therapy uses the photosensitizer porfimer sodium (Photofrin^®) and red laser light. It may be used to treat esophageal and lung cancers, and it’s currently being studied for use with other cancers.

Photodynamic therapy for cancer

PDT is used to treat a variety of cancers and precancers.

It may relieve the symptoms of some cancers, such as esophageal cancer blocking the throat or lung cancer blocking the airways. It may also destroy the blood vessels that provide oxygen and nutrients to a tumor.

When PDT destroys cancer cells, it seems to trigger the body’s immune system to attack the cancer, even if it’s in other parts of the body.

Because the light used in PDT doesn’t travel far into the body, this treatment is traditionally only an option for cancers that are:

• At or near the surface of the skin
• On or near the surface of a membrane on the inside of a body cavity (like the bladder)
• In an orifice (like inside the throat or bladder)

PDT isn’t useful for large tumors because it can’t penetrate inside them more than one-third of an inch.

Photodynamic therapy for skin cancer

Because doctors may easily access the skin for treatment, PDT is an option for many skin cancers. Generally, as long as the skin cancer tumor is relatively thin and isn’t melanoma, it may be a candidate for PDT. Some examples of skin cancers that a doctor might treat with light therapy include:

• Actinic keratosis, a precancerous skin condition that a doctor may treat with blue light phototherapy when it’s on the face or scalp
• Thin basal cell carcinoma, which is typically treated twice per cycle, with seven days of healing between sessions
• Bowen’s disease, a precancerous skin condition
• Thin squamous cell carcinoma 

Lung cancer photodynamic therapy

PDT may be a treatment option for non-small cell lung cancer (NSCLC) tumors that are:

• Small and early stage
• In both lungs
• Not operable
• Growing back after surgery
• In patients who can’t tolerate an anesthetic or operation

This treatment may help reduce advanced cancer symptoms, such as coughing, breathlessness and coughing up blood.

Photodynamic therapy for head and neck cancer

In the esophagus (the tube that leads from the throat to the stomach), red light therapy with porfimer sodium may be an option for:

• Barrett’s esophagus, a precancerous thickening of the mucous membranes around the esophagus caused by excess stomach acid
• Early esophageal cancer

It may also be an option for cancers of the voice box and other areas of the throat. This approach may be appropriate for many types of head and neck cancers, particularly the superficial, spreading cancers, as well as cancers that have metastasized to these areas.

In advanced head and neck cancers that block the esophagus, PDT may help ease issues with swallowing, allowing the patient to eat normally.

Photodynamic therapy for prostate cancer

The prostate is a small organ located near many blood vessels and nerves essential to urinary and sexual function. Research shows that PDT may be appropriate for prostate cancer. This option also has fewer side effects and effects on urinary and erectile function.

PDT isn’t currently a standard therapy for prostate cancer, but the research is promising, though more studies are needed. PDT is different from radiation therapy and chemotherapy because it doesn’t damage DNA. It’s also less likely to result in metastasis or cause the patient to become resistant to other drug treatments (called therapy cross resistance). For these reasons, PDT for prostate cancer is an active research area.

Photodynamic therapy for bladder cancer

PDT may be an option for treating cancers that develop in the lining of the bladder, which is a unique, hollow organ. By threading a small tube with an attached camera and light through the urethra, doctors may treat cancerous areas directly.

The photosensitizer may also make the cancer cells emit light, allowing doctors to see them. Research has shown that this approach works well in treating bladder cancers. Clinical trials are ongoing.

PDT may be an option for treating bladder cancers that:

• Have come back after other therapies
• Are widely spread over the inside of the bladder
• Aren’t responding to standard treatment
• Are in patients who aren’t candidates for surgery

Photodynamic therapy for bile duct cancer

PDT is often used to help reduce symptoms of bile duct cancer, but not as a first-line or standard treatment. It may also stop tumors from growing through a stent, a tube placed to enable bile to reach the digestive tract.

Doctors may reach cancers that develop in the bile duct with an endoscope through the stomach and small intestines.

Researchers are still determining which PDT options should be used for bile duct cancer.

What to expect during photodynamic therapy

The care team may perform PDT as an outpatient procedure, either alone or in combination with other cancer treatments.

PDT is performed in two steps. First, the photosensitizer is applied by mouth, directly on the skin or through an IV. Normal cells and cancer cells pick up the drug from the bloodstream, but it sticks around longer in the cancer cells. Then, the patient receives the light activation therapy.

The time between taking the drug and receiving the light treatment is called the drug-to-light interval. It varies based on the drug. It may be anywhere from hours to days.

How the care team applies light depends on where the cancer is located. If the tumor is on the skin, they’ll aim the laser or LED directly at the cancer cells. If it’s down the throat—in the esophagus, airways or lungs—a doctor will use a thin tube with a camera and the treatment light to access the areas.

If PDT is being used for a white blood cell cancer called cutaneous T-cell lymphoma, the doctor may remove and treat the blood outside the body. They mix the blood with the photosensitizer and then blast it with light to target the abnormal blood cells. The blood is then reinfused into the patient’s body in a procedure called extracorporeal photopheresis (ECP).

Photodynamic therapy side effects

PDT side effects differ based on the photosensitizers used, the type of light used and the tumor’s location.

Once a patient takes the photosensitizer, they must stay out of the sun and bright lights for up to six weeks. If exposed to too much light, the skin may become swollen, sunburned or blistered.

Generally, the treated area may:

• Turn red
• Swell
• Develop blisters
• Feel burnt
• Be painful
• Scar
• Change color
• Itch or sting

If the treated area is in the throat, swelling may cause trouble breathing or swallowing.

Sometimes, instead of stimulating the immune system, PDT may weaken it. Rarely, skin cancers may develop where the doctor applies the treatment.

Side effects typically improve or go away after treatment stops.