Mesothelioma: Diagnostic and Therapeutic Challenges
A mesothelioma is a malignancy of the tissues that line both the lung surface and the inside of the chest wall. These thin membranes—the parietal pleura lining the chest and the visceral pleura doing the same to each lung—occasionally develop a cancer called mesothelioma. More than 80% are caused by exposure to asbestos an historically common insulating material used to line walls in homes and offices. There is no known other causative agent.
Patients first notice some combination of chest pain and/or shortness of breath. The tumor invading the chest wall and irritating nerves causes the pain. Fluid builds up as the abnormal pleura secrete more and absorb less. The fluid collapses the sponge-like lung and the patient experiences difficulty in breathing. Early evaluation with chest x-ray and CT scan of the chest are abnormal but not diagnostic. Typical findings include a pleural effusion (fluid in the chest but outside the lung) and thickening of the pleurae.
As for any disease, diagnosis must precede treatment. Initial evaluation, aimed at obtaining a specific diagnoses, can include thoracentesis (using a needle or catheter to evacuate as much fluid as possible). If analysis of the fluid is not diagnostic the next step is to biopsy suspicious lesions using either thoracoscopy (a minimally invasive surgical technique to visualize the interior of the chest) or a radiologically controlled needle biopsy through the chest wall.
Diagnosis confirmed, staging of the tumor follows to determine its extent. An operation is performed if a battery of scans shows the tumor is so localized the it can all be removed. The subsequent procedure is quite extensive and requires the surgeon to remove the entire lung together with the entire parietal pleura and the tissue it contacts such as the pericardium surrounding the heart and the diaphragm. Unfortunately the tumor is rarely completely resectable and an operation that leaves cancer behind means the operation was futile as the cancer will inexorably spread. Attempts to shrink the tumor with chemotherapy sufficiently to allow successful surgery have only infrequently been successful.
Treatment today is primarily the use of chemotherapy that does usually prolong life but is not curative. The search for more efficacious therapies continues. There are two on the horizon. One is the use of agents which attack the blood supply to the mesothelioma. These antiangiogenic drugs prevent the tumor from developing new blood vessels to support its growth. Also in trials are immunotherapeutic agents aimed to harness the body’s own immune system to combat the malignancy.
