Mesothelioma is a rare form of cancer that can develop after exposure to asbestos. This cancer grows in the mesothelium, or the lining around an organ. There is currently no known cure for mesothelioma, but researchers have developed an increasing number of treatments to extend survival time. One of the most promising experimental treatments is mesothelioma photodynamic therapy. This treatment harnesses the power of light to kill cancer cells.
Mesothelioma photodynamic therapy has been used, so far, on the two most common mesothelioma types: pleural mesothelioma, which forms on the pleura, the lining around the lungs; and peritoneal mesothelioma, which affects the lining on the inside of the abdomen. On rare occasions, mesothelioma can develop in the lining around the heart (pericardial) and the lining of the testicles (testicular) as well.
What is Photodynamic Therapy?
You may hear photodynamic therapy called by several different names: PDT, photochemotherapy, phototherapy, or photoradiation therapy. This emerging treatment is often used to treat skin diseases such as acne and psoriasis and skin cancers such as melanomas. It is also used to treat an eye condition called macular degeneration. It has been approved to treat several types of cancer as well, including cancer of the esophagus (the tube that connects your mouth to your stomach). It is also gaining recognition as an effective treatment for mesothelioma.
PDT works by administering photosensitizing chemicals to the tumor, then shining a light on the area. The light activates the chemicals, which create a reactive form of oxygen called singlet oxygen. The new oxygen molecules kill off cancerous cells.
The photosensitizer can be administered intravenously or applied directly to the treatment site. When it’s given systemically, you have to wait a few days to shine a light on the tumor area. In that time, normal cells will shed the photosensitizing chemical, while cancer cells will absorb it. This waiting time, which is called the drug-to-light interval, means that a minimum number of healthy cells will be harmed by the treatment. If the tumor is not on the skin, the light is applied to the area through a tube or by surgically exposing the tumor area.
Each photosensitizing agent is paired with a particular type of light, which activates it. The most common intravenous photosensitizer is porfimer sodium, which is marketed under the trade name Photofrin. Photofrin Is used with a red laser light.
If the treatment area is on the skin, a photosensitizing agent may be applied directly to the area to be treated. This technique can also be used during surgery, when your doctor has direct access to the tumor area and can apply light to the area after removing or debulking your mesothelioma tumor.
An agent that may be applied to your tumor during surgery is a type of chlorin that is commonly known as mTHPC and sold under the brand name Foscan. This compound is a stronger photosensitizer than Photofrin, so it can be used at lower doses and needs less light to become activated.
Because cancer cells grow so quickly, they need a large supply of nutrients. Tumors stimulate the growth of extra capillaries to feed themselves. PDT treatment can have the side benefit of damaging these blood vessels. PDT has also been found to stimulate the body’s own immune response, in some cases.
Mesothelioma Photodynamic Therapy
PDT doesn’t work for every type of cancer. If a tumor is large, PDT won’t be able to penetrate beneath the surface layer, so it won’t be very effective. If the cancer is in a part of the body where it is difficult to shine a light, PDT may not work there either.
Some of the first internal cancers to be treated with PDT were in areas like the lungs, where a fiber optic tube could be inserted down the bronchial tubes to provide the light needed to complete the treatment. As researchers refine the technique, they are finding more applications for this therapy.
Why is Photodynamic Therapy Good for Mesothelioma?
Studies have found that mesothelioma photodynamic therapy can extend life expectancy with few side effects. This treatment works especially well for mesothelioma patients because the space between the layers of the mesothelium allows space to shine a light on the cancerous cells.
Who Can Receive Mesothelioma Photodynamic Therapy?
Mesothelioma photodynamic therapy is most effective in the earlier stages of the cancer. It won’t work on a large tumor or on cancer that has spread to other parts of the body. Unlike chemotherapy, which can kill cancer cells throughout your system, PDT can work only on a localized cancer growth.
Some patients can’t tolerate the photosensitizing chemicals. People with some types of blood diseases, especially those classified as porphyrias, cannot be treated with PDT.
Even if you have a large mesothelioma tumor, however, you may be a candidate for mesothelioma photodynamic therapy. PDT is often combined with other treatments, including surgery, which can reduce the size of your tumor to the point where PDT will work well. Mesothelioma photodynamic therapy can be an excellent adjuvant or add-on treatment with surgery or chemotherapy.
What Are the Benefits of Mesothelioma Photodynamic Therapy?
Mesothelioma photodynamic therapy has fewer side effects than chemotherapy or surgery. In addition, PDT may be able to rid your body of microscopic cancer cells that other treatments have missed.
PDT is an inexpensive treatment, especially when compared to surgery. It can be performed as an outpatient treatment, so you won’t have to spend hours or days in the hospital during treatment.
Limits of Mesothelioma Photodynamic Therapy
Because mesothelioma photodynamic therapy is relatively new, this treatment is not available at every hospital that treats mesothelioma patients.
In addition, mesothelioma photodynamic therapy has one major side effect: sensitivity to light. After treatment, you will need to spend several weeks avoiding exposure to the sun and strong lights. More on this side effect below.
Types of Mesothelioma Photodynamic Therapy
Mesothelioma photodynamic therapy can be administered during surgery or as a separate treatment, often after surgery or chemotherapy. It is unlikely that you will receive PDT as a standalone treatment. Clinical trials have found that photodynamic therapy can work well in combination with other mesothelioma treatments.
Intraoperative Photodynamic Therapy
When PDT is administered to the tumor area while it is exposed during surgery, this is called intraoperative photodynamic therapy.
It’s important to knock out as much of the cancer as possible during treatment because stray cancer cells can form new tumors or migrate to other organs and develop metastatic cancer. When cancer metastasizes, it is even more dangerous and difficult to treat than the original tumor, so preventing metastases is an important factor in mesothelioma treatment.
Combining surgery with mesothelioma photodynamic therapy can solve problems that each of these treatments would have if used alone. PDT can’t penetrate through thick tissues, so it isn’t effective in attacking a bulky tumor. Surgeries sometimes remove a lot of tissue, even one of your lungs, as a precaution and to take out as much mesothelioma as possible. Very intensive surgeries require longer recovery times. Some patients are not strong enough to undergo these surgeries in the first place.
When mesothelioma photodynamic therapy is combined with surgery, your surgeon may be able to leave more of your organs intact while still killing off the maximum number of cancerous cells.
There are two common types of surgery for pleural mesothelioma. Extrapleural pneumonectomy or EPP is a radical surgery that removes not only the pleura but also part of the diaphragm and the lining around the heart (pericardium), as well as the lung next to the mesothelioma tumor. While this surgery does a good job of removing any tissues that might be harboring malignant mesothelioma cells, it leaves you with only one lung. The recovery from this procedure is long and physically challenging.
A newer and more common surgery for pleural mesothelioma is a pleurectomy/decortication or P/D. This operation is called lung-sparing surgery, because it only removes the pleura and surrounding tissue while leaving both lungs intact. The surgeon carefully examines the lung and removes as much potentially cancerous tissue from the lung surface during the decortication part of the procedure.
When intraoperative mesothelioma photodynamic therapy is paired with P/D surgery, there is even less reason to resort to the more drastic EPP procedure. First, your surgeon will complete the pleurectomy to remove the tumor and any tissue where the tumor has spread. If you didn’t receive an intravenous photosensitizer such as Photofrin before surgery, a topical photosensitizer will be applied to your lungs. Then your surgeon will shine a light on the exposed area to activate the chemical reaction that kills off mesothelioma cancer cells.
Radiation therapy is another choice for intraoperative multimodal mesothelioma treatment. PDT is more experimental but it may be preferable to radiation because the light causes less damage to healthy lung tissue.
One early study showed that intraoperative PDT using Foscan was effective in extending survival for patients with diffuse malignant mesothelioma, which is an especially malicious form of the disease because it spreads out and invades surrounding tissues. Since then, PDT has evolved from being considered risky and experimental to being accepted by many in the mesothelioma treatment field as an effective part of a multimodal mesothelioma treatment plan.
Intraoperative mesothelioma photodynamic therapy can also be used during peritoneal mesothelioma surgery. This form of the disease is treated with debulking or cytoreductive surgery. This surgery is often accompanied by a special chemotherapy treatment called hyperthermic intraperitoneal chemotherapy or HIPEC. PDT provides another option to reduce the number of cancerous cells in your abdomen with minimal side effects.
Mesothelioma Photodynamic Therapy as an Outpatient Treatment
PDT may also be administered as an outpatient treatment, either after surgery or in combination with chemotherapy.
For this form of mesothelioma photodynamic treatment, you will receive an intravenous photosensitizer such as Photofrin before your treatment. It takes a few days (the drug-to-light interval) for your healthy cells to shed the photosensitizing agent and for it to concentrate in your cancerous cells. At that point, you are ready to receive PDT.
During your treatment, a flexible tube called an endoscope will be inserted into the area of the tumor. This requires a very small incision, so this procedure does not require much recovery time.
At the end of the endoscope is a light that will activate the photosensitizer and set off the chemical reaction that will kill your cancerous mesothelioma cells.
Side Effects of Mesothelioma Photodynamic Therapy
Mesothelioma photodynamic therapy has fewer side effects than most cancer treatments. Other than swelling in the area that receives the treatment, you are unlikely to experience the nausea, fatigue, and pain that can accompany chemotherapy and surgery.
However, there is one big precaution that you must take as soon as you receive the photosensitizing agent and for a few weeks afterward, or you may experience very unpleasant and serious side effects.
Sensitivity to Light
While you have the photosensitizing agent in your system, your whole body will be light sensitive. Sunlight or even bright indoor lights can cause your skin to blister and swell, like a bad sunburn.
If you got the agent intravenously, you will need to take precautions and avoid bright light for at least 30 days after treatment and possibly up to three months. Your doctor will give you a test to see if you are still photosensitive. You will need to avoid bright light until your doctor clears you.
For topical, intraoperative PDT, your light sensitivity may be more short-lived. Check with your doctor to make sure.
You don’t have to sit in a completely dark room during this time, but you will need to make some changes to protect yourself from harm. To avoid burning your skin, take these precautions:
- Stay inside with shades drawn and skylights covered. Don’t let any sunlight into your house.
- If you must go out, wear clothing that completely covers your body, including a hat with a brim, sunglasses, and gloves. Wear clothing made of fabric with a tight weave to completely block the sun. Sunscreen will not protect against the type of rays that your skin is sensitive to during PDT.
- Try to do any outside activities after sunset. At the very least, avoid going out during the middle of the day when the sun is the most intense.
- Avoid bright indoor lights and heat. Stay away from the kinds of lights that doctors and dentists use in their exam rooms and use a low setting on your hair dryer.
- Stay away from surfaces like beaches or snowy streets that reflect a lot of light.
The Future of Mesothelioma Photodynamic Therapy
The future of mesothelioma photodynamic therapy is bright. Researchers continue to develop more effective photosensitizing drugs. Interstitial photodynamic therapy may allow the treatment of larger tumors without surgery, by using medical imaging to help doctors insert tiny fiber optic tubes and shine light into the middle of a larger tumor.
Photoimmunotherapy or PIT is another exciting frontier in mesothelioma treatment. PIT uses specially targeted photosensitizers to add photodynamic therapy to immunotherapy to attack certain types of malignant tumors.
Some mesothelioma photodynamic therapy treatments are still in the experimental phase. Ask your doctor whether you might qualify for a clinical trial to receive this cutting-edge therapy.