Abstract

Lung cancer is the most common cancer globally, and tobacco smoking is well established as the main cause. Yet occupational exposures play an important role among exposed workers, especially jointly with smoking. The SYNERGY project was established in 2007 to estimate joint effects of asbestos, respirable crystalline silica, polycyclic aromatic hydrocarbons, chromium/nickel and smoking in the development of lung cancer. Sixteen case-control studies conducted between 1985 and 2010 from Canada, Europe, New Zealand and China were pooled, including 19 370 lung cancer cases and 23 674 controls with detailed information on tobacco habits and lifetime occupations. Controls were recruited from the general population (81%) or hospitals (19%), and were individually or frequency matched to cases by sex and age. Information was predominantly collected by interviews with the study participants themselves, though next-of-kin respondents were accepted in five of the studies if subjects were unavailable (9.1% of cases, 6.6% of controls). The database comprises around 14% never smokers, whereof 822 cases. Women represent around 20% or the study population. A quantitative job exposure matrix (SYN-JEM) was created based on exposure measurements from multiple countries together with auxiliary data, covering a time period of more than 50 years. SYN-JEM is based on statistical models that predict job-, time-, and region-specific exposure levels. Cumulative exposures (e.g. ff/ml-years) were calculated for each subject by linking SYN-JEM with individual occupational histories. Unconditional logistic regression models were used to estimate odds ratios (OR), 95% confidence intervals (CI), and trends. The strengths of SYNERGY includes bringing together epidemiologists and exposure assessment experts from around the world to advance occupational cancer epidemiology, 2) power to study small risks, 3) providing quantitative exposure estimates for population-based case-control studies, and 4) allowing sub-group analyses, e.g. by gender, histology and smoking status.