Pleural Plaques and the Risk of Lung Cancer in Asbestos-exposed Subjects.

Abstract

Asbestos exposure is associated with a dose-dependent risk of lung cancer. The association between lung cancer and the presence of pleural plaques remains controversial. To define the relationship between pleural plaques and lung cancer risk. Subjects were from two cohorts: (1) crocidolite mine and mill workers, and Wittenoom township residents and (2) a mixed asbestos fiber, mixed occupation cohort. All subjects underwent annual review since 1990, chest x-ray (CXR) or low dose computed tomography (LDCT) scan and outcome linkage to national cancer and mortality registry data. Cox regression, with adjustment for age (as the underlying matching time variable), was used to estimate hazard ratios for lung cancer incidence by sex, tobacco smoking, asbestos exposure, and presence of asbestosis and pleural plaques. For all 4240 subjects, mean age at follow up was 65.4 years, 3486 (82.0%) were male, 1315 (31.0%) had pleural plaques and 1353 (32.0%) had radiographic asbestosis. 3042 (71.7%) were ever-smokers with mean tobacco exposure of 33 pack-years. 200 lung cancers were recorded. Risk of lung cancer increased with cumulative exposure to cigarettes, asbestos and presence of asbestosis. Pleural plaques did not confer any additional lung cancer risk in either cohort (cohort 1: HR 1.03, 95% CI 0.64-1.67, p=0.89; cohort 2: HR 0.75, 95% CI 0.45-1.25, p=0.28). The presence of pleural plaques on radiological imaging does not confer an additional increase in the risk of lung cancer. This result is consistent across two cohorts with differing asbestos fiber exposures and intensity.