Mesothelioma Photodynamic Therapy
Photodynamic therapy or PDT uses laser light to kill cancer cells. The Food and Drug Administration (FDA) has approved its use for non–small cell lung cancer and cancer of the esophagus. However, photodynamic therapy is in the early experimental stages as a possible mesothelioma treatment.
Photodynamic therapy involves injection of light-sensitive molecules into the pleural space. These are taken up by the tumor cells, which then have intense light beams directed at them, resulting in their death. In good-risk patients with small malignant mesothelioma, photodynamic therapy has been moderately successful, although complications may occur with poorly directed light.
In combination with surgical procedures, photodynamic therapy has not improved survival or local disease control. Furthermore, it has damaging effects on normal and healing tissues, and the post-operative death rates may be high. It is therefore not likely to become standard treatment for malignant mesothelioma.
How Photodynamic Therapy Works
The patient receives a photosensitizing agent or photosensitize, which is a drug that makes the cancer cells vulnerable and sensitive to light of specific wavelengths. The photo sensitizer collects in the cancerous cells. Depending upon its type, the photo sensitizer either does not collect in the healthy cells or is eliminated from these cells more rapidly than from the cancer cells.
After the cancer cells have been sensitized, fiber–optic cables are placed in the body (usually through open–chest surgery) in order to focus light of just the right frequency on the tumor. This causes the photo sensitizer to react with oxygen to produce a toxic molecule that kills the cancer cell.
Photodynamic therapy has been used on an experimental basis during surgery to help prevent the recurrence of mesothelioma cancer in the lining of the lungs or pleura. In one clinical trial of 26 patients, photodynamic therapy was combined with either of two types of surgery—a pleurectomy or an extrapleural pneumonectomy. A pleurectomy is the removal of lining of the lung or pleura. The more extensive extrapleural pneumonectomy involves removal of both the lung and pleura. The photo sensitizer was Foscan (meta–tetrahydroxyphenylchlorin, mTHPC).
The researchers pointed out that the use of photodynamic therapy might allow some patients to undergo a lung–sparing pleurectomy rather than the more invasive extrapleural pneumonectomy. Currently, other studies are exploring the interaction of surgery and photodynamic therapy using the photo sensitizer perfumer sodium, a drug commonly used in photodynamic treatment of non–small cell lung cancer that affects the bronchi
Intraoperative photodynamic therapy is a new type of treatment that uses special drugs and light to kill cancer cells during surgery. A drug that makes cancer cells more sensitive to light is injected into a vein several days before surgery. During surgery to remove as much of the cancer as possible, a special light is used to shine on the pleura. This treatment is being studied for early stages of mesothelioma in the chest.
