Malignant pleural mesothelioma is an uncommon, but no longer rare, cancer that is frequently difficult to diagnose and poorly responsive to therapy. Because of the difficulties distinguishing mesothelioma from metastatic adenocarcinoma and reactive pleural inflammation, thoracoscopy or open lung biopsy are usually required to obtain adequate samples for pathologic evaluation. Staging of mesothelioma remains a controversial area. Because none of the six staging systems used in the past was found to be predictive, a TNM-based staging system was recently proposed and is awaiting universal acceptance. Generally perceived as a death sentence, this cancer is associated with a median survival of 9 months from the time of diagnosis in most series, but newer therapeutic strategies show promise for improved and even long-term survival in select cases. Randomized trials are awaited to determine if the improvements in survival reported are not simply due to patient selection.
Abbreviations:CT computed tomography, MRI magnetic resonance imaging, TNM primary tumor, regional lymph nodes, and distant metastasis
More than 2,000 cases of malignant pleural mesothelioma are diagnosed in the United States each year. The most recent estimates based on incidence data from the Surveillance, Epidemiology, and End Results Program predict that the annual number of mesothelioma cases for males will peak this year at nearly 2,300 . These numbers are expected to then fall as the number of persons alive who were occupationally exposed to asbestos falls. Although there is no doubt that asbestos causes mesothelioma, a clear history of asbestos exposure is not always obtained, with series reporting a history of exposure in 20–90% of cases (mean: 70%) [2–4]. Determination of the true incidence of asbestos-related cases is made especially difficult because there is no defined threshold of exposure, and it is estimated that asbestos fibers may be found in the lungs of 90% of urban dwellers [5,6]. Further confounding all this is the recent discovery of simian-virus 40 (SV40)-like sequences in some human mesothelioma cells by Pass et al . SV40 has been shown to induce mesotheliomas in hamsters and is known have contaminated the polio vaccine administered from 1955 through 1961. However, another group did not detect any SV40 DNA in any of the 50 mesotheliomas they evaluated , and thus far an epidemiologic impact has not been determined .
Although the risk of developing mesothelioma rises with the amount of exposure, it is clear that genetic factors play a role in determining who develops the disease because not all persons exposed to high levels of asbestos dust develop mesothelioma. This conclusion is supported by the work of Roggli et al.. They compared the number of asbestos fibers found in the lungs of patients who died of mesothelioma and patients who died of other causes, and they determined that fiber numbers did not correlate with development of disease.
Groups especially at risk for significant exposure to asbestos and, therefore malignant mesothelioma, include  :
Workers in the asbestos industry
Household contacts of asbestos workers
Maintenance and repair workers in buildings with asbestos insulation
There is no evidence to support an increase in incidence of mesothelioma related to cigarette smoking .
Ralph H. Johnson VA Medical Center and the Center for Molecular and Structural Biology, Medical University of South Carolina, Charleston, South Carolina, USA
Correspondence to: Alice M. Boylan, Ralph H. Johnson VA Medical Center and the Center for Molecular and Structural Biology, Medical University of South Carolina, 171 Ashley Avenue, Charleston, SC 29425, USA.