Cigarette smoking and risk of death from colorectal cancer in women

Much of the epidemiological evidence concerning the relationship between cigarette smoking and colorectal cancer has come from studies in men, and less is known about the role of smoking in the aetiology and pathogenesis of colorectal cancer in women. Therefore, the purpose of the present study was to investigate the association between cigarette smoking and risk of death from colorectal cancer in a large cohort of women.

The study was conducted within the cohort of 56 837 women who were enrolled in the Canadian National Breast Screening Study (NBSS) and who completed self-administered dietary questionnaires. (The NBSS is a randomized controlled trial of screening for breast cancer in women aged 40-59.) During follow up to December 31, 1993, 90 women died from colorectal cancer (79 from colon cancer, 11 from rectal cancer). Deaths were ascertained by means of record linkage to the Canadian Mortality Database. Cox proportional hazards models were used to estimate hazards ratios (HR) and 95% confidence intervals (CI) for the association between cigarette smoking and risk of death from colorectal cancer, after adjustment for age alone, or age, energy intake, alcohol consumption, and other potentially relevant confounders.

Cigarette smoking was not associated with altered risk of death from colorectal cancer. The multivariate HR (95% CI) for the risk in ever smokers compared with that in never smokers was 1.37 (0.86-2.18). There was no evidence for trends in risk with cigarette-years of consumption, and by amount and duration of consumption.

The results of this study suggest that cigarette smoking is not associated with altered risk of death from colorectal cancer in women. However, given the possibility that the association between cigarette smoking and colorectal cancer might not become evident until at least 30-40 years after the commencement of smoking, it might still be too early to detect an association, since uptake of smoking by women occurred later than uptake by men.