Malignant Mesothelioma Following Radiation

Abstract

The strong association between asbestos exposure and malignant mesothelioma has been widely accepted since 1960 (1,2). Although asbestos is the primary etiologic agent for this tumor, a significant number of patients who develop mesothelioma have no known asbestos exposure. Radiation, nonasbestos mineral fibers, organic chemicals, chronic inflammation (3), and simian virus 40 (SV40) exposure (4,5) have also been suggested as risk factors for mesothelioma in humans. Because asbestos is ubiquitous, past exposures are often difficult to quantitate. Past asbestos exposure may be assessed by a standardized questionnaire that collects information on occupational, paraoccupational, environmental, and domestic contact with asbestos from insulation, mining, milling, heating trades, shipyard work, and construction (6). However, the long latency period of 20 years or longer from the onset of exposure to the development of malignant mesothelioma likely influences the accuracy of the exposure information obtained (1). More objective evidence of asbestos exposure includes radiologic findings such as bibasilar fibrosis and calcified pleural plaques, the presence of asbestos fibers in sputum or bronchoalveolar lavage samples, and evidence of interstitial fibrosis or ferruginous bodies in lung tissue (7). These criteria have been used to try to exclude asbestos as the causal factor in some cases of mesothelioma. In published case series, the proportion of mesothelioma cases that have an asbestos exposure history ranges from 16% to 77% (8). Of 668 patients who died of malignant mesothelioma in Canada and the United States from 1960 to 1975, only 50% of men and 5% of women had known asbestos exposure (9). Occupational asbestos exposure in women and children is rare; therefore, most asbestos exposure in these individuals is thought to come from a household member who is employed in an asbestos industry. The occurrence of malignant mesothelioma in children may not be related to asbestos at all. In a report of 13 children diagnosed with mesothelioma in the United States, the short latency period from the time of exposure to tumor development and the absence of geographic clustering argued against an environmental