Risk factors shared by COPD and lung cancer and mediation effect of COPD: two center case-control studies.

PURPOSE: To reveal the shared risk factors for chronic obstructive pulmonary disease (COPD) and lung cancer, and to analyze the mediation effect of COPD during lung carcinogenesis. METHODS: We conducted four independent case-control studies included 1,511 COPD patients and 1,677 normal lung function controls and 1,559 lung cancer cases and 1,679 cancer-free controls during 2002-2011 in southern and eastern Chinese. RESULTS: Eight factors were observed to be consistently associated with both diseases risk, including pre-existing tuberculosis, smoking, passive smoking, occupational exposure to metallic toxicant, poor housing ventilation, biomass burning, cured meat consumption, and seldom vegetables/fruits consumption. Furthermore, smoking and biomass burning conferred significantly higher risk effects on lung cancer in individuals with pre-existing COPD than those without. COPD also had significant mediation effects during lung carcinogenesis caused by smoking, passive smoking, and biomass burning, which explained about 12.0 % of effect, 3.8 % of effect, and 6.1 % of effect of these factors on lung tumorigenesis in turn. CONCLUSION: Our study mapped a shared spectrum of etiological factors for both COPD and lung cancer in Chinese, and COPD acts as a mediator during lung cancer development. These observations should be in consideration for the prevention of both diseases.