Photodynamic therapy, also called PDT, is a cancer treatment that uses light energy to kill cancer cells. First, the doctor administers a photosensitizer, a type of drug that makes cells sensitive to certain wavelengths of light. Then the cancer cells are exposed to light, causing a reaction that kills cancer cells nearby.
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In clinical trials, researchers found that this treatment can improve life expectancy in pleural mesothelioma patients, especially when used in combination with other treatments such as surgery.
The main photosensitizer used for pleural mesothelioma treatment is porfimer sodium, usually called Photofrin. The Food and Drug Administration (FDA) approved this drug for use in other cancers, such as esophageal cancer, and recognized its potential in treating mesothelioma. Because Photofrin may help treat the rare cancer, the FDA designated it an orphan drug, which helps speed along the FDA approval process.
Photodynamic therapy is usually an outpatient procedure and does not require a hospital stay. It may be used in conjunction with other treatments like chemotherapy and surgery to fight the cancer in multiple ways.
The treatment begins with the administration of a photosensitizing agent, which is injected into the bloodstream. This drug is absorbed by cells, both healthy and cancerous, but stays in cancerous cells longer. After one to three days, the photosensitizer has left most healthy cells but remains in mesothelioma cells. This is when light is administered, usually via laser, to activate the photosensitizer. Doctors may insert fiber optic cables into the lungs in order to aim the light at the tumor and directly hit cancer cells, a process that may take up to an hour.
This light must be at a specific wavelength and color in order to trigger a reaction within the drug. Photofrin, for example, reacts to red light. Once the drug is activated, it produces a highly reactive form of oxygen. The oxygen affects all nearby cancer cells, prompting them to die. It may also damage the tumor's blood vessels, thus cutting off the nutrient supply and killing cancer cells.
Photodynamic therapy can only be used on areas of the body that light can reach, such as just below the skin or along the lining of internal organs. Because of this, the therapy is most effective in treating localized cancer that has not spread throughout the body. In addition, individuals with large tumors may not be suitable candidates for this therapy, as the light is unable to penetrate the entire tumor.
This treatment causes skin and eye sensitivity to light for about six weeks. Doctors advise patients to avoid sunlight and other bright light during this time. PDT may cause swelling, burning, pain or scarring in healthy tissues. Patients may also experience coughing, trouble swallowing, stomach pain, painful breathing or shortness of breath.
Studies of photodynamic therapy in pleural mesothelioma patients have been successful in recent years, but some early studies showed no improvement when PDT was used. In a 1996 study, 63 pleural mesothelioma patients underwent surgery and chemotherapy, and half were randomly selected to receive PDT as well. Based on the addition of PDT, researchers found no significant difference in survival times. Patients lived a median of 14.1 months without PDT and 14.4 months with it.
A 2004 study showed a substantial improvement in survival times when photodynamic therapy was added to surgery. Patients treated with surgery alone lived a median of 10 months, while patients treated with surgery and PDT survived a median of 13 to 14 months. Researchers concluded that the therapy showed promise in successfully treating mesothelioma and must be studied further.
Encouraging clinical trial results have led some of the country's top cancer centers to offer photodynamic therapy to their patients. The Abramson Cancer Center in Pennsylvania and the Stanford Cancer Institute in California have this therapy available for mesothelioma patients who qualify for it. Brigham and Women's Hospital, renowned for its mesothelioma program, is also equipped for PDT but does not normally use it in mesothelioma treatment.
Medical researchers seek to improve the efficacy of PDT and use it in more types of cancer, including peritoneal mesothelioma. Researchers hope to develop photosensitizers that specifically target cancer cells and have more toxic reactions. Doctors also hope to find a more effective means of administering the necessary light so that it can penetrate tissue and treat larger tumors.
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