Int J Cancer. 2020 Aug 5. doi: 10.1002/ijc.33248. Online ahead of print.
Smoking has been consistently associated with the risk of colorectal cancer (CRC) in Western populations; however, evidence is limited and inconsistent in Asian people. To assess the association of smoking status, smoking intensity, and smoking cessation with colorectal risk in the Japanese population, we performed a pooled analysis of ten population-based cohort studies. Study-specific hazard ratios (HR) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards model and
then pooled using a random effects model. Among 363,409 participants followed up for 2,666,004 person-years, 9,232 incident CRCs were identified. In men, compared with never smokers, ever smokers showed higher risk of CRC. The HRs (95% CI) were 1.19 (1.10-1.29) for CRC, 1.19 (1.09-1.30) for colon cancer, 1.28 (1.13-1.46) for distal colon cancer, and 1.21 (1.07-1.36) for rectal cancer. Smoking was associated with risk of CRC in a dose-response manner. In women, compared with never smokers, ever smokers showed increased risk of distal colon cancer (1.47 [1.19-1.82]). There was no evidence of a significant gender difference in the association of smoking and CRC risk. Our results confirm that smoking is associated with an increased risk of CRC, both overall and subsites, in Japanese men and distal colon cancer in Japanese women. This article is protected by copyright. All rights reserved.