Pleural plaques and the risk of pleural mesothelioma.

BACKGROUND The association between pleural plaques and pleural mesothelioma remains controversial. The present study was designed to examine the association between pleural plaques on computed tomography (CT) scan and the risk of pleural mesothelioma in a follow-up study of asbestos-exposed workers. METHODS Retired or unemployed workers previously occupationally exposed to asbestos were invited to participate in a screening program for asbestos-related diseases, including CT scan, organized between October 2003 and December 2005 in four regions in France. Randomized, independent, double reading of CT scans by a panel of seven chest radiologists focused on benign asbestos-related abnormalities. A 7-year follow-up study was conducted in the 5287 male subjects for whom chest CT scan was available. Annual determination of the number of subjects eligible for free medical care because of pleural mesothelioma was carried out. Diagnosis certification was obtained from the French mesothelioma panel of pathologists. Survival regression based on the Cox model was used to estimate the risk of pleural mesothelioma associated with pleural plaques, with age as the main time variable and time-varying exposure variables, namely duration of exposure, time since first exposure, and cumulative exposure index to asbestos. All statistical tests were two-sided. RESULTS A total of 17 incident cases of pleural mesothelioma were diagnosed. A statistically significant association was observed between mesothelioma and pleural plaques (unadjusted hazard ratio (HR) = 8.9, 95% confidence interval [CI] = 3.0 to 26.5; adjusted HR = 6.8, 95% CI = 2.2 to 21.4 after adjustment for time since first exposure and cumulative exposure index to asbestos). CONCLUSION The presence of pleural plaques may be an independent risk factor for pleural mesothelioma.