Background and Objectives: Research shows that the lung cancer risk from concurrent exposure to certain workplace carcinogens and tobacco smoking is greater than the additive effect of each exposure alone highlighting opportunities for targeted workplace cancer prevention. However, existing evidence relies on crude ever/never exposure estimates, and it is unclear how well these risks are communicated by occupational health professionals, particularly to high-smoking-prevalence groups such as blue-collar workers. The SMOX pilot study aimed to more accurately estimate these joint effects by studying the interaction between various quantitative occupational exposures and tobacco smoking, and to assess the current knowledge and practices of occupational health professionals and smoking habits and motivations among construction workers about these effects.
 
Methods: We used data from the SYNERGY project, including 13,605 lung cancer cases and 16,451 male controls with detailed smoking and occupational histories. These occupational histories were then linked to job exposure matrices to assign occupational exposure to asbestos, respirable crystalline silica (RCS), chromium VI, polycyclic aromatic hydrocarbons (PAH) and diesel engine exhaust. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression models. Joint effects were assessed on the additive scale by calculating the relative excess risk due to interaction (RERI) and its 95% CI. In parallel, two surveys were conducted in the Auvergne–Rhône-Alpes region: an online survey of 331 occupational health professionals and face-to-face interviews with 207 construction workers. Descriptive analyses were then performed.
 
Results: There was an increasing risk of lung cancer for all the occupational carcinogens of interest and for smoking even at low exposure levels, with OR varying from 1.15 for PAH to 1.30 for RCS. When occupational exposures were low and the workers were light-smokers, the RERIs were not elevated. However, current and recent former smokers with higher exposure levels generally experienced elevated RERI (>5 for asbestos). The RERIs were not elevated for former smokers over 20 years, unless highly or moderately exposed.
The survey of occupational health professionals showed that, apart from the joint effects of asbestos and smoking, their knowledge was limited about other occupational carcinogens’ joint effect with smoking, and less than one third systematically informed workers about these effects. Two thirds of the construction workers surveyed claimed not having access to information on the risks of smoking in their workplace. Finally, 53% of workers with an education level below the high school diploma felt that “knowing about the increased health risks of smoking around workplace carcinogens” was not a sufficient motivation to quit smoking.
 
Conclusions: Our results show that joint effects between occupational lung carcinogens and smoking are particularly high among current smokers and remain high years after cessation, suggesting that subgroups of workers could benefit most from future targeted public health interventions. However, as the two surveys reported, there is a need to disseminate this information more effectively among high-risk workers in collaboration with occupational health professionals and to reduce exposure to occupational carcinogens where such exposure persists.