For thousands of years, people have used light to treat skin diseases. Photodynamic therapy, also called PDT and phototherapy, uses medicine activated by light to treat cancer.
It's already being used for cancers of the skin, esophagus, and lung. Now researchers are studying it as a treatment for ovarian cancer.
Why Treat Ovarian Cancer With Light?
Ovarian cancer can be hard to control because it has often already spread by the time it's diagnosed. Surgery and chemotherapy are two of the main treatments, but not everyone is a good candidate for surgery, and the cancer almost always comes back after treatment.
Photodynamic therapy (PDT) is a promising way to kill ovarian cancer cells. Researchers are looking at whether adding PDT to surgery and chemo might help these treatments work better against ovarian cancer. PDT might also be used as palliative medicine, to relieve the symptoms of late-stage ovarian cancer.
Photodynamic therapy has the advantage of targeting cancer cells more precisely than chemotherapy. It's also less toxic to healthy cells. But it does have a few risks.
How Does PDT Work?
Photodynamic therapy uses a drug called a photosensitizing agent that is activated by light to kill cancer cells. The light comes from an intense laser beam, a light-emitting diode (LED), or another special light source.
When the drug absorbs light, it produces an active form of oxygen that kills cancer cells. The treatment also damages blood vessels that supply the cancer with oxygen and nutrients. And it might stimulate the immune system to attack the cancer.
When Is It Used?
PDT is only approved to treat certain types of cancer, including:
- Head and neck cancer
- Cancers of the stomach and esophagus
- Non-small-cell lung cancer
- Basal and squamous cell skin cancers
- Precancers like actinic keratosis and Barrett esophagus
Researchers are studying photodynamic therapy as a treatment for ovarian cancer. It might also help relieve symptoms when the cancer has spread to the lining of the abdominal wall, called the peritoneum.
How Do You Get Photodynamic Therapy?
Photodynamic therapy is usually an outpatient procedure, which means you go home on the same day instead of staying overnight in the hospital. You may get this treatment at the same time as surgery, chemotherapy, or radiation therapy.
First, you get a photosensitizer drug by mouth or through an IV into a vein. The drug travels all over your body and collects in your cells. It stays in cancer cells much longer than in healthy cells.
After you get the drug, you have to wait for it to build up in your cancer cells. Doctors call this waiting period the drug-to-light interval.
In about 1 to 3 days, you go back to the hospital. The doctor threads a scope into your body and puts a thin strand of glass called a fiber-optic cable through the scope. For ovarian cancer, the drug may be given through the peritoneum – the lining of the abdominal cavity. The fiber-optic cable shines light on the cancer cells that have absorbed the medicine.
What Are the Benefits?
Photodynamic therapy is a more targeted treatment than chemotherapy. Because the photosensitizer collects for longer in cancer cells than in normal cells, there is less damage to healthy cells.
This treatment is also less invasive than surgery. And you can have it done again in the same spot if it doesn't kill all of the cancer cells the first time.
What Are the Drawbacks?
The light can't reach very deeply into your body or your organs. It works better for cancers that are on the lining of organs than on tumors inside the organ. It's also not as effective for larger tumors.
Photodynamic therapy is considered safe, but it can cause side effects like:
- Skin redness, swelling, and pain
- Blisters
- A burning, itchy, or tingling feeling in the treated area
Rarely, this treatment weakens the immune system for a short period of time.
Not everyone will have these side effects. If you do have any side effects, your doctor can offer advice on how to manage them. Any problems you do have should go away after you finish treatment.
The drug used in PDT makes your skin very sensitive to light. You'll have to avoid the sun and bright light for about 6 weeks after your treatment. If you do go outside, wear protective clothes and a wide-brimmed hat to shield your skin.
How Well Does It Work?
It's hard to know how well photodynamic therapy works for ovarian cancer, because most of the studies have been done on cancer cells in a lab, or in animals.
In a study of rats, photodynamic therapy killed ovarian cancer cells and reduced blood vessel growth to the tumor. Rats with ovarian cancer in their peritoneum lived longer after treatment with PDT plus the drug clofibric acid than rats that didn't get this treatment.
Results in humans haven't been as positive. When researchers gave PDT to people whose ovarian cancer had spread to their peritoneum, the cancer came back after treatment in most cases.
Researchers are looking at whether PDT might work better combined with other treatments like surgery or chemotherapy. One study found that adding the chemo drug cisplatin to photodynamic therapy killed more ovarian cancer cells in a lab.
Studies are also testing out new kinds of photosensitizing drugs. A light-sensitive drug containing folate killed many types of ovarian cancer cells in a lab. The drug also stimulated immune cells. These results need to be confirmed in humans.
How Do I Get This Treatment?
Photodynamic therapy isn't approved to treat ovarian cancer, but you may be able to try it by enrolling in a clinical trial. If you're interested, ask your oncologist if they know of any photodynamic therapy studies for ovarian cancer.
Before you enroll in any study, make sure you understand how the treatment might help your cancer, and what side effects it could cause.
