Asbestos, Asbestosis, Smoking, and Lung Cancer. New Findings from the North American Insulator Cohort

Abstract

Asbestos, smoking, and asbestosis increase lung cancer risk in incompletely elucidated ways. Smoking cessation among asbestos-exposed cohorts has been little studied. To measure the contributions of asbestos exposure, asbestosis, smoking, and their interactions to lung cancer risk in an asbestos-exposed cohort and to describe their reduction in lung cancer risk when they stop smoking. We examined lung cancer mortality obtained through the National Death Index for 1981 to 2008 for 2,377 male North American insulators for whom chest X-ray, spirometric, occupational, and smoking data were collected in 1981 to 1983 and for 54,243 non-asbestos-exposed blue collar male workers from Cancer Prevention Study II for whom occupational and smoking data were collected in 1982. Lung cancer caused 339 (19%) insulator deaths. Lung cancer mortality was increased by asbestos exposure alone among nonsmokers (rate ratio = 3.6 [95% confidence interval (CI), 1.7-7.6]), by asbestosis among nonsmokers (rate ratio = 7.40 [95% CI, 4.0-13.7]), and by smoking without asbestos exposure (rate ratio = 10.3 [95% CI, 8.8-12.2]). The joint effect of smoking and asbestos alone was additive (rate ratio = 14.4 [95% CI, 10.7-19.4]) and with asbestosis, supra-additive (rate ratio = 36.8 [95% CI, 30.1-45.0]). Insulator lung cancer mortality halved within 10 years of smoking cessation and converged with that of never-smokers 30 years after smoking cessation. Asbestos increases lung cancer mortality among nonsmokers. Asbestosis further increases the lung cancer risk and, considered jointly with smoking, has a supra-additive effect. Insulators benefit greatly by quitting smoking.