Emerging tobacco-related cancer risks in China: A nationwide, prospective study of 0.5 million adults

Abstract

Background: In China, cigarette consumption has increased substantially since the 1980s, almost exclusively in men. This study was aimed at assessing the emerging cancer risks.

Methods: A nationwide, prospective study recruited 210,259 men and 302,632 women aged 30 to 79 years from 10 areas of China from 2004 to 2008; approximately 18,000 incident cancers were recorded during 7 years of follow-up. Cox regression yielded adjusted risk ratios (RRs) comparing smokers (including those who had stopped because of illness but not those who had stopped by choice) with never-smokers.

Results: Among men, 68% were smokers; their overall cancer risk was significantly increased (RR, 1.44; 95% confidence interval [CI], 1.37-1.53), and it was greater in urban (RR, 1.55; 95% CI, 1.41-1.70) than in rural areas (RR, 1.39; 95% CI, 1.30-1.49). This excess accounted for 23% of all cancers between the ages of 40 and 79 years, with significantly elevated risks of lung cancer (RR, 2.51; 95% CI, 2.18-2.90), liver cancer (RR, 1.32; 95% CI, 1.12-1.54), stomach cancer (RR, 1.34; 95% CI, 1.16-1.55), esophageal cancer (RR, 1.47; 95% CI, 1.24-1.73), and an aggregate of 5 other minor sites (RR, 1.52; 95% CI, 1.25-1.86). For lung cancer, the RRs were much greater for nonadenocarcinoma (RR, 5.83; 95% CI, 5.02-6.77) than for adenocarcinoma (RR, 1.78; 95% CI, 1.36-2.34). Among exsmokers (6.7%) who had stopped by choice, there was little excess cancer risk approximately 15 years after quitting. Among the few female smokers (3%), the overall cancer risk was also significantly increased (RR, 1.42; 95% CI, 1.28-1.57). Smoking was estimated to cause approximately 435,000 new cancers per year in China (approximately 360,000 in men and approximately 75,000 in women).

Conclusions: In China, smoking now causes a quarter of all adult male cancers. High male uptake rates before the age of 20 years and nearly universal use of cigarettes foreshadow substantial tobacco-attributed risks in China unless there is widespread cessation.

Keywords: China; cancer; cessation; cohort study; smoking.

Figure 1

Prevalence of ever regular smoking by year of birth among men and women.

Figure 2

Adjusted risk ratios for (A) all cancer and (B) lung cancer by the age at which smoking was started and by the amount last smoked in urban and rural men. The adjusted risk ratios are plotted on floating absolute scales. The area of each black square is inversely proportional to the variance of the log risk ratio, which also determines the 95% confidence intervals (CIs).

Figure 3

Adjusted risk ratios (RRs) for (A) all cancer and (B) lung cancer by the number of years stopped smoking among male exsmokers who had stopped by choice. The adjusted RRs are plotted on floating absolute scales. The area of each black or white square is inversely proportional to the variance of the log RR, which also determines the 95% confidence intervals (CIs).