Photodynamic therapy is an emerging cancer treatment that uses a drug called a photosensitizer and a particular kind of light to kill cancer cells. The application of photodynamic therapy or PDT to pleural mesothelioma is still in its infancy. But the results of early research are encouraging.
In a June 2011 study published in the Annals of Thoracic Surgery, pleural mesothelioma patients who underwent lung-sparing surgery in combination with photodynamic therapy, showed unusually long overall survival, University of Pennsylvania researchers reported.
Malignant pleural mesothelioma is an aggressive cancer of the lining of the lung associated with inhaling asbestos. Asbestos exposure typically occurs 20 to 50 years before symptoms of mesothelioma appear. But once the aggressive asbestos-related cancer develops, patients typically die within 9 to 12 months.
The Penn researchers compared the survival of two groups of pleural mesothelioma patients who underwent different surgical treatments combined with photodynamic therapy and chemotherapy from 2004 to 2008. A number of the mesothelioma patients who underwent photodynamic therapy in combination with a pleurectomy to remove cancerous tissue from the lining of the lung remained alive after more than two years, they reported.
The strategy of any multi-pronged cancer treatment regimen is to use surgery to remove cancerous tumors as completely as possible, then use other therapies to control any remaining cancer cells.
The way photodynamic therapy works is a drug is injected into the patient that makes cancer cells sensitive to certain wavelengths of light. The specific wavelength of light causes the photosensitzers to release a form of oxygen that kills cells—in this case malignant mesothelioma cells. The light beam can penetrate into tissue, but cannot pass through more than about one-third inch of tissue. That makes photodynamic therapy more suitable for treatment of cancers on the surface or just under the surface of tissue.
To date, the U.S. Food and Drug Administration has approved PDT to treat esophageal cancer non-small cell lung cancer. The use of light-based therapy in treatment of mesothelioma is still experimental, and the University of Pennsylvania is one of only a few institutions using PDT for mesothelioma treatment.
In the study, one group of 14 mesothelioma patients underwent a modified version of radical surgery to remove a lung and the lining of the lung, a procedure known as an extrapleural pneumonectomy. The radical surgery was combined with the light-based cancer therapy while each patient was in the operating room. The second group of 14 mesothelioma patients underwent a pleurectomy, in which the diseased lining of the lung is removed, but the patient’s lung itself is spared.
The two groups totaling 19 men and 9 women overall had similar demographics, and both groups received the photodynamic therapy. The patients ranged in age from 27 to 81 years old. Most patients also received pemetrexed-based chemotherapy and some underwent radiation.
There was a significant difference in the overall survival of the two groups of patients, the researchers reported.
The median survival for the patients who underwent the extrapleural pneumonectomy to remove a lung combined with the light therapy was about 8.4 months. But enough of the mesothelioma patients in the second group who underwent lung-sparing surgery remained alive after two years that the researchers have yet to be able to calculate their median survival. That contrasts with the typical survival of 9 months to 13 months for mesothelioma patients who undergo a pleurectomy based on other studies.
The findings are particularly notable because most of the patients in the study had advanced stage III and IV cancer. They would not otherwise have been good candidates for radical surgery because of their age or cancer characteristics.
Given the results, the Penn researchers say that removal of the cancerous lining of the lung (a radical pleurectomy ) combined with photodynamic therapy is a reasonable option for appropriate pleural mesothelioma patients. A growing body of evidence supports photodynamic therapy as an effective way to induce an immune system response against cancer. The researchers say the procedure can serve as the backbone of multi-pronged surgery-based treatments for mesothelioma.
A follow-up study involving multiple medical research institutions and the latest generation of photosensizer drugs is now underway to test the hypotheses produced by this study.