Journal
of the National Cancer Institute, Vol. 92, No. 23, 1888-1896, December 6, 2000
© 2000 Oxford University Press
Cigarette Smoking and Colorectal Cancer Mortality in the
Cancer Prevention Study II
Affiliation of authors: Epidemiology and Surveillance Research, American Cancer Society, Atlanta, GA.
Correspondence to: Ann Chao, Ph.D., Epidemiology and
Surveillance Research, American Cancer Society, 1599 Clifton Rd., N.E., Atlanta,
GA 30329–4251 (e-mail: achao@cancer.org).
Background:
Recent studies suggest that long-term cigarette smoking is
associated with an increased risk of colorectal cancer. Whether the association
is causal or due to confounding remains unclear. Methods: We
examined cigarette smoking in relation to colorectal cancer
mortality, evaluating smoking duration and recency and controlling
for potential confounders in the Cancer Prevention Study II. This
prospective nationwide mortality study of 1 184 657 adults (age 
30 years) was begun by the American Cancer Society in
1982. After exclusions, our analytic cohort included 312 332 men and
469 019 women, among whom 4432 colon or rectal cancer deaths
occurred between 1982 and 1996 among individuals who were cancer
free in 1982. Rate ratios (RRs) and 95% confidence intervals (CIs)
were estimated by fitting Cox proportional hazards models. All
statistical tests were two-sided. Results:
Multivariate-adjusted colorectal cancer mortality rates were highest
among current smokers, were intermediate among former smokers, and
were lowest in lifelong nonsmokers. The multivariate-adjusted RR
(95% CI) for current compared with never smokers was 1.32
(1.16–1.49) among men and 1.41 (1.26–1.58) among women. Increased
risk was evident after 20 or more years of smoking for men and women
combined as compared with never smokers. Risk among current and
former smokers increased with duration of smoking and average number
of cigarettes smoked per day; risk in former smokers decreased
significantly with years since quitting. If the
multivariate-adjusted RR estimates in this study do, in fact,
reflect causality, then approximately 12% of colorectal cancer
deaths among both men and women in the general U.S. population in
1997 were attributable to smoking. Conclusions: Long-term
cigarette smoking is associated with increased risk of colorectal
cancer mortality in both men and women. Clear reduction in risk is
observed with early smoking cessation.