Abstract
A207
Differences were seen in the associations between smoking exposure and lung cancer risk across ethnic groups in the Multiethnic Cohort (MEC) (Haiman et al., NEJM 2006). Smoking has been suggested to increase the risk of colorectal cancer and the strength of this association may also vary according to race or ethnicity. We investigated the association between cigarette smoking and colorectal cancer among African American, Native Hawaiian, Latino, Japanese American and Caucasian men and women participating in the Multiethnic Cohort Study. This prospective cohort study included 215,251 residents of Hawaii and Los Angeles, aged 45-75 at baseline. The present analysis was based on 191,011 subjects and included 1,138 male and 972 female incident colorectal cancer cases, identified through 2001. Cigarette smoking was modeled by indicator variables for former and current smoking, years of duration and average number of cigarettes smoked per day. Among men, the association between smoking and risk varied by ethnicity (p<0.0001 and p=0.01 for duration and dose, respectively). Risk of colorectal cancer was not found to be associated with smoking in African-American, Native Hawaiian or Caucasian men. In Japanese Americans, the relative risk (RR) and 95% confidence interval (CI) was 1.94 (1.05-3.58)), and 2.44 (1.25-4.76) for 31-40 years and ≥41 years of smoking, respectively, compared to never smokers, p-trend <0.0001. No association was found with increasing dose [RR = 0.76 (95% CI: 0.44-1.29) for ≥31 cigarettes per day; p-trend 0.59]. In contrast, among Latino men, duration was not as strong a predictor [RR = 2.05 (95% CI: 0.75-5.62) for ≥41 years of smoking; p-trend: 0.25] as was dose [RR = 4.41 (95% CI: 1.87-10.4) for ≥31 cigarettes per day; p-trend 0.02]. Unlike for men, in women, risk of cigarette smoking did not differ by race/ethnicity. Prolonged smoking was found to increase risk of colorectal cancer [RR for ≥41 years of smoking vs. never smoker = 1.87 (95% CI 1.11-3.16; p-trend 0.09)]. Compared to never smokers, colorectal cancer risk may be increased by prolonged smoking in Japanese American men and by heavy smoking in Latino men. No evidence of association with smoking was found for Caucasian, African American or Native Hawaiian men. Long-term smoking may increase colorectal cancer risk in women regardless of racial or ethnic background.
[Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006]