Photodynamic therapy (PDT) uses light to kills cancer cells.
The therapy is often used after mesothelioma surgery.
PDT has few side effects, though clinical trials continue to test the therapy.
PDT has been shown to increase patient survival, with some living 36 months.
Photodynamic therapy (PDT) may be recommended as an additional treatment option for patients with mesothelioma. The emerging therapy is used for pleural mesothelioma patients and can be applied following radiation therapy, chemotherapy or surgical resection as part of a multimodal treatment plan.
What is Mesothelioma Photodynamic Therapy?
Mesothelioma photodynamic therapy is a non-invasive outpatient treatment option that can be added to a multimodal treatment plan. The therapy involves the combination of three innocuous elements that work together to target and kill malignant mesothelioma cells.
- A light source
- Oxygen (in the tissue)
- A photosensitizing agent (commonly Photofrin)
PDT begins with the injection of the photosensitizing agent into the bloodstream so it will be absorbed by cells. Healthy cells eliminate the agent at a faster rate than cancerous cells. Because of this difference, the therapy can be highly targeted and does not negatively impact healthy tissue, ultimately leading to fewer side effects and a better recovery for the patient.
After the healthy cells have processed the photosensitizer, about 24 to 72 hours after injection, the patient will be exposed to a light source. The laser light is administered over the course of anywhere from 5 to 40 minutes, varying based on tumor size. Depending on the number and size of tumors, the treatment may be repeated several times to effectively kill the tumor cells. Mesothelioma specialists have found repeated treatment with PDT does not compound toxicity for patients, meaning patients won’t see more side effects.
After the PDT treatment, patients may return to the outpatient facility to have the cancerous tissue removed. For pleural mesothelioma patients, this procedure is done through bronchoscopy, a tube inserted down the throat and into the lungs.
Eligibility for Photodynamic Therapy
Photodynamic therapy has limited risks but isn’t a suitable treatment option for all mesothelioma patients. Patients are ineligible if they have:
- A fistula (an abnormal connection between organs)
- An allergy to the photosensitizing agent
- A tumor that involves a major blood vessel
- Enlarged veins
Patients may also be ineligible for PDT if their tumors are deep within the skin, extremely large or have metastasized. If any of these three elements are present, the therapy is not viable because the light source used to activate the photosensitizing agent cannot penetrate the body very far. The light treatment only travels through tissue about one centimeter thick. To combat this limitation, patients may receive intraoperative photodynamic therapy, which allows the light to be administered during thoracic surgery, giving easier access to tumors.
Additionally, PDT with Photofrin has only received Food and Drug Administration (FDA) approval for the treatment of non-small cell lung cancer (NSCLC) and esophageal cancer. Mesothelioma patients seeking treatment with PDT must participate in clinical trials. These trials may have additional requirements that patients must meet to be eligible for PDT treatment.
Risks of Photodynamic Therapy
There are very few risks associated with mesothelioma photodynamic therapy, as it is such a targeted treatment. While limited, patients should still understand the potential complications with this and any treatment types before making any treatment decisions.
Side effects vary slightly depending on the photosensitizing agent used and the area of the body being treated. Most common for mesothelioma patients is PDT therapy using Photofrin or porfimer sodium, though there are also newer PDT drugs being tested for various cancers. The most common side effect with Photofrin PDT therapy is light sensitivity. This causes patients to be highly susceptible to burning, blistering and swelling from exposure to natural and artificial light sources. Depending on an individual’s reaction, light sensitivity may last anywhere from 30 days to three months, so patients should prepare to mitigate risks.
How to Combat Light Sensitivity
- Before treatment, cover all windows and skylights in your home.
- Make sure you’re fully covered when leaving treatment and any other time you’re outside. Bring sunglasses, gloves, long sleeves, long pants and a wide-brimmed hat with you to treatment.
- After treatment, limit time outdoors between 10 a.m. and 4 p.m. When necessary, run errands after sundown.
- Continue to fully cover yourself anytime you go outdoors. Sunscreen will not protect from PDT light sensitivity, so full-coverage light-colored clothing is necessary.
The other most common side effect from PDT is swelling, which may lead to chest or back pain and breathing difficulties. However, the swelling is typically temporary. The more serious complications are less frequent and rarely occur.
Less Common Side Effects of Photodynamic Therapy
- Acute respiratory distress
- Atrial fibrillation
- Chyle leak (injury to the thoracic duct)
- Deep vein thrombosis
- Hyperpigmentation and scarring
- Pulmonary embolism
- Skin cancer
Success Stories following Mesothelioma Photodynamic Therapy
Photodynamic therapy for cancer is a relatively new and still emerging treatment modality. Early research does show promising results for mesothelioma patients, including low toxicity, improved life expectancy and quality of life.
Photodynamic therapy has been proven effective when added to other treatment modalities including extended pleurectomy/decortication (eP/D) and proton therapy (PT). One 2018 study analyzed malignant pleural mesothelioma patients who underwent a trimodal treatment plan with eP/D, PDT and PT. The patients within the study achieved 90% local control of disease and 56% of study participants survived for one year or longer. The researchers believe that using the PDT may have improved the efficiency of the following proton therapy. Reports show that PDT causes the body’s immune system to be more susceptible to immunogenic responses, such as PT. The ability to safely combine three mesothelioma treatments with no high-grade toxicity is encouraging and offers hope to patients who may not have found success with more traditional treatment approaches like chemotherapy.
Researchers also found an improved overall survival time in a clinical trial testing the efficacy of a radical pleurectomy followed by PDT for pleural mesothelioma patients. The 38 participants achieved an overall median survival time of 31.7 months. Those participating in the study with epithelial mesothelioma achieved even longer survival. For that subgroup, median overall survival was 41.2 months. The average life expectancy for pleural mesothelioma patients is six months to one year with standard therapies.
Mesothelioma patients interested in adding PDT to their treatment regime should discuss the possibility with a mesothelioma specialist to see if they’re a candidate for the therapy. Patients should be sure to understand all their treatment options, including potential benefits and risks, before making any treatment decisions.