Photodynamic therapy (PDT) is a treatment that uses special drugs activated by light to treat cancer. It's called a "focal therapy" because it focuses on cancer cells while sparing healthy cells. The idea behind PDT is to wipe out as much of the cancer as possible without causing a lot of side effects.
So far, photodynamic therapy is approved to treat some cancers of the skin, esophagus, and lungs. It's also a promising treatment for small, low-risk prostate cancers that aren't likely to spread outside the prostate gland.
Photodynamic therapy has a few advantages over current treatments for early-stage prostate cancer. Some men don't want to wait through active surveillance, which closely monitors but doesn't treat the cancer. Others worry about the sexual and urinary side effects that surgery and radiation can cause.
PTD might one day be an alternative to these treatments. But for now, it's still considered experimental.
How Does Photodynamic Therapy Kill Cancer Cells?
Photodynamic therapy, also known as phototherapy, uses medicines called photosensitizing drugs to make prostate cancer cells more sensitive to light. It's a two-part treatment.
First, the medicine is injected into a vein through an IV. The drug travels through the blood to the prostate gland, where the cancer cells absorb it.
The second part of the treatment happens hours or days later. A special wavelength of light is aimed at the prostate gland. One way to get light to the right place is by inserting very thin strands of light called optical fibers into the prostate. An ultrasound projects an image of the prostate on a video screen so the doctor can find the prostate and place the fibers.
When light activates the drug, it produces a type of oxygen called a free radical that kills the cancer cells.
Photodynamic therapy also treats cancer in other ways. It shrinks the blood vessels that deliver blood to "feed" the cancer. And it might alert the immune system to attack the cancer.
How Well Does It Work?
Photodynamic therapy works about as well as surgery or radiation therapy for some types of cancer, but it's still being researched for prostate cancer. We don't yet know how safe and effective it is compared with other prostate cancer treatments, but studies so far have been promising.
One review of 14 studies included more than 650 people with slow-growing prostate cancers. Over half of those who had photodynamic therapy showed no signs of cancer on a biopsy afterward. Thirty-five percent of people in the study had a drop in prostate-specific antigen (PSA) level following treatment. PSA is a measurement of prostate cancer growth.
One downside of photodynamic therapy is that it's hard to get the light into deeper areas of the body, like the prostate gland. And the treatment works better in some people than in others. Researchers are studying different types of drugs and light sources to see which ones are most effective against prostate cancer.
This treatment may be an option for men with intermediate-risk prostate cancers that haven't spread outside of their prostate. For men with low-risk prostate cancer, active surveillance (monitoring) is preferred because their cancer is likely to grow slowly, and photodynamic therapy can increase the risk for urinary and erection problems. There isn't enough evidence to show that this treatment helps with higher-risk prostate cancers.
Next, researchers want to find out whether photodynamic therapy works against slightly larger prostate cancers.
Photodynamic Therapy Pros
Photodynamic therapy is much more precise than surgery and radiation therapy. The medicine builds up in cancer cells much more than in healthy ones, which helps to limit damage and side effects. PDT also doesn't leave scars.
Unlike active surveillance, photodynamic therapy is a treatment. Research shows that prostate cancer is less likely to spread in people who have PDT compared to those who have active surveillance.
Prostate cancer sometimes becomes resistant to hormone therapy or other treatments. This means the treatment no longer works against the cancer. Prostate cancer is less likely to become resistant to photodynamic therapy, so you can get this treatment more than once.
Photodynamic Therapy Cons
The light from photodynamic therapy can't reach very deeply into the skin. That's why it works best for skin cancers or other cancers that are near the surface. It may not work as well for tumors that are inside the body, like prostate cancer.
Photodynamic therapy also doesn't work for everyone. Some people will need surgery or radiation afterward to slow or stop their cancer.
Side Effects of Photodynamic Therapy
Photodynamic therapy is less likely to cause urinary or erection side effects than surgery or radiation. But it could make the skin more sensitive to light. People who have this treatment will need to protect their skin by staying out of sunlight or direct light and by wearing sun-protective clothing and a hat when they do go outside.
Photodynamic therapy can also cause these skin side effects:
Treating prostate cancer with photodynamic therapy can cause problems like:
- Blood in the urine
- Trouble controlling erections, or erectile dysfunction
- Burning when you pee
- Problems emptying your bladder, or urinary retention
These side effects should improve soon after you finish the treatment.
How Do You Get This Treatment?
Photodynamic therapy isn't approved to treat prostate cancer. It's only available in clinical trials right now. Researchers are still trying to figure out which medicine works best, how much light to use, and how to reach deeper areas of the body like the prostate.
If you're interested in trying this treatment, you can ask the doctor who treats your prostate cancer if you're a good candidate for a clinical trial of photodynamic therapy.
