Objectives To examine the joint association of smoking and silica dust exposure with lung cancer risk.
Method This is a population-based case-referent study among Hong Kong Chinese males. We consecutively recruited 1208 newly diagnosed lung cancer cases and 1069 age-matched community referents during the period 2004–2006. We obtained each participant’s lifelong smoking data, occupational history, and other important information including family cancer history. Unconditional multiple logistic regression analysis was performed to estimate the odds ratio (OR) and the 95% confidence interval (95% CI). We examined the joint association and tested potential interaction under multiplicative or additive risk model.
Results A total of 132 (10.9%) lung cancers and 536 (50.1%) community referents were never smokers. The prevalence of silica dust exposure among ever smokers was higher than the never smokers for both the lung cancers (13.5% vs. 7.6%) and community referents (6.4% vs. 3.7%). A 2.4-fold (95% CI: 1.05–5.52) risk of lung cancer for silica dust exposure was observed in never smokers, whilst it increased sharply to 12-fold (95% CI: 7.59–18.95) if the dust exposed workers were also smokers. A possible additive interaction was indicated between these two exposures but power is limited (synergy index = 1.61, 95% CI: 0.95–2.73), particularly for the adenocarcinoma (synergy index = 1.25, 95% CI: 0.52–3.01).
Conclusions Our findings supports the conclusion of IARC that workers exposed to silica dust increase lung cancer risk but adds new evidence on a positive additive interaction between silica and smoking. [Research Grants Council (Project CUHK4460/03M), Hong Kong].
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