Department of Epidemiology, American Cancer Society, Atlanta, Georgia 30303-1002, USA.
Cancer Epidemiol Biomarkers Prev. 2009 Dec;18(12):3362-7. doi: 10.1158/1055-9965.EPI-09-0661.
Many studies have reported a 20% to 60% increase in risk of colorectal cancer associated with active smoking. However, neither the U.S. Surgeon General nor the IARC have classified the relationship as causal because of concern about residual confounding.
In a prospective study of 184,187 people followed from 1992 to 2005, we used Cox proportional hazard models to examine the relationship of cigarette smoking to incident colorectal cancer, controlling for screening and multiple known and putative risk factors. Information on smoking and time-varying covariates was updated in 1997, 1999, 2001, and 2003.
The incidence of colorectal cancer was significantly higher in current [hazard ratios (HR), 1.27; 95% confidence intervals (CI), 1.06-1.52] and former smokers (HR, 1.23; 95% CI, 1.11-1.36) compared with lifelong nonsmokers in analyses that controlled for 13 covariates, including screening. The relative risk was greatest among current smokers with at least 50 years of smoking (HR, 1.38; 95% CI, 1.04-1.84). Among former smokers, risk of colorectal cancer decreased with greater time since cessation (P trend = 0.0003), and also decreased with earlier age at cessation (P trend = 0.0014). No association was seen among former smokers who had quit before age of 40 years or abstained for 31 years or more.
Long-term cigarette smoking is associated with colorectal cancer, even after controlling for screening and multiple other risk factors.
许多研究报告称，与不吸烟者相比，主动吸烟者患结直肠癌的风险增加 20%至 60%。然而，由于担心残余混杂因素，美国外科医生总署和国际癌症研究机构都没有将这种关系归类为因果关系。
在一项对 184187 人的前瞻性研究中，我们使用 Cox 比例风险模型来研究吸烟与结直肠癌发病的关系，同时控制了筛查和多个已知和潜在的危险因素。吸烟和时变协变量的信息于 1997 年、1999 年、2001 年和 2003 年进行了更新。
在控制了 13 个协变量（包括筛查）的分析中，与终生不吸烟者相比，当前吸烟者（危险比[HR]，1.27；95%置信区间[CI]，1.06-1.52）和前吸烟者（HR，1.23；95%CI，1.11-1.36）的结直肠癌发病率显著升高。在至少吸烟 50 年的当前吸烟者中，相对风险最高（HR，1.38；95%CI，1.04-1.84）。在以前的吸烟者中，随着戒烟时间的延长（P 趋势=0.0003），结直肠癌的风险降低，且戒烟年龄越早（P 趋势=0.0014），风险也越低。在 40 岁之前戒烟或戒烟 31 年以上的前吸烟者中，没有发现关联。
即使在控制了筛查和多个其他危险因素后，长期吸烟仍与结直肠癌相关。
