Smoking and lung cancer in China: combined analysis of eight case-control studies

Smoking is well established as a principal risk factor for lung cancer. The risk of lung cancer is about ten times higher in smokers in Western countries. In China, a number of epidemiological studies have investigated the association between lung cancer and smoking and in the present paper, a combined analysis of eight such case-control studies is described. The summary odds ratio (OR), calculated by the Mantel-Haenszel method, and attributable risk (AR) of lung cancer associated with smoking were calculated from the combined data which were obtained from a literature review. The eight case-control studies were conducted in Beijing, Shanghai, Shenyang, Nanjing, Harbin, Zhengzhou, Taiyuan, and Nanchang, yielding a total of 4081 lung cancer cases and 4338 controls. The summary OR of lung cancer associated with smoking was 2.17 (95% CI (confidence interval): 1.98-2.39). The OR were 3.09 (95% CI: 2.61-3.66) for males and 2.30 (95% CI: 1.96-2.69) for females. The AR were 38.2% for both sexes, 56.7% for males and 25.5% for females. Risks of 1.00, 1.03, 2.04, and 3.33 showed a dose-response relationship between lung cancer and number of cigarettes smoked per day. There were also significant dose-response relationships of lung cancer with duration of smoking (OR = 1.00, 1.02, 2.66), and age at start of smoking (OR = 1.00, 3.30, 2.36, 1.18). The OR and AR of lung cancer associated with smoking in China were much lower than those reported in Western countries and the possible reasons for this are discussed.