8287191 Joint effects of occupational exposure to asbestos or respirable crystalline silica and tobacco smoking on lung cancer risk

<h3>Objective</h3> To explore joint effects of occupational exposure to asbestos and respirable crystalline silica (RCS) and smoking on lung-cancer risk. <h3>Material and Methods</h3> This analysis in men included 13,605 lung-cancer cases and 16,451 controls from 14 European and Canadian case-control studies. Job histories were linked to SYN-JEM to assign occupational exposure to asbestos and RCS. Various metrics of smoking and occupational exposure to asbestos and RCS were investigated in relation to lung cancer risk using unconditional logistic regression models. Odds ratios (ORs) and 95% confidence intervals (CIs) were adjusted for study centre, age group, and ‘recognized high-risk occupations’. Joint effects were evaluated on the additive scale by calculating the relative excess risk due to interaction (RERI) and corresponding 95% CI using the delta-method. <h3>Results</h3> Occupational cumulative exposure to asbestos &lt;median (1.2 fibres/ml-years) and cumulative smoking ≤20 pack-years (py) show RERI: 0.37, CI -0.21 to 0.94. Individuals, with asbestos exposure &gt;median have a RERI: 1.67, CI 1.06 to 2.29. Cumulative asbestos exposure results in positive RERIs, whether &lt;median (RERI: 1.50, CI 0.19 to 2.81) or &gt;median (RERI: 3.70, CI 2.31 to 5.08), with cumulative smoking &gt;20py. Occupational cumulative exposure to RCS &lt;median (1.1 mg/m3-years) and cumulative smoking ≤20py shows RERI: 0.80, CI 0.17 to 1.43, and RERI: 1.84, CI 1.04 to 2.64 for RCS &gt;median. When RCS &lt;median, the RERI is 2.97, CI 1.40 to 4.55, and 4.56, CI 2.92 to 6.21 when RCS &gt;median with smoking &gt;20py. <h3>Conclusion</h3> Occupational exposure to RCS and smoking confers an excess lung-cancer risk beyond additivity even at cumulative exposure levels below median and light smoking. Occupational exposure to asbestos and smoking shows a similar pattern, except a small RERI at cumulative exposure to asbestos below median and light smoking. These findings emphasize the need for proactive control of occupational exposures and prevention of tobacco smoking.