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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 > or =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. [ABSTRACT FROM AUTHOR]

Background: Several studies have reported positive associations between environmental tobacco smoke (ETS) and increased risk of breast cancer. However, studies of active smoking and risk of breast cancer are equivocal and in general do not support a positive association. To try to resolve this paradox, we examined the association between breast cancer mortality and potential ETS exposure from spousal smoking in an American Cancer Society prospective study of U.S. adult women.Methods: We assessed breast cancer death rates in a cohort of 146 488 never-smoking, single-marriage women who were cancer free at enrollment in 1982. Breast cancer death rates among women whose husbands smoked were compared with those among women married to men who had never smoked. Cox proportional hazards modeling was used to control for potential risk factors other than ETS exposure.Results: After 12 years of follow-up, 669 cases of fatal breast cancer were observed in the cohort. Overall, we saw no association between exposure to ETS and death from breast cancer (rate ratio [RR] = 1.0; 95% confidence interval [CI] = 0.8-1.2). We did, however, find a small, not statistically significant increased risk of breast cancer mortality among women who were married before age 20 years to smokers (RR = 1. 2; 95% CI = 0.8-1.8).Conclusions: In contrast to the results of previous studies, this study found no association between exposure to ETS and female breast cancer mortality. The results of our study are particularly compelling because of its prospective design as compared with most earlier studies, the relatively large number of exposed women with breast cancer deaths, and the reporting of exposure by the spouse rather than by proxy. [ABSTRACT FROM AUTHOR]

Background: The results of several recent epidemiologic studies suggest that estrogen replacement therapy (ERT) in postmenopausal women may decrease their risk of subsequently developing colon or colorectal cancer. However, the association is not clear, as other similar studies have failed to show this inverse relationship.Purpose: The present study attempts a more definitive analysis of the relationship between fatal colon cancer and use of ERT among women in a large prospective study of adults in the United States.Methods: Women were selected for study from the 676,526 female participants in Cancer Prevention Study II (CPS-II), a prospective mortality study of about 1.2 million American men and women (from all 50 states, the District of Columbia, and Puerto Rico), begun by the American Cancer Society in 1982. The median age of the female CPS-II participants was 56 years in 1982. Vital status was determined through December 31, 1989; 630,585 participants (93.2%) were still alive and 43,862 (6.5%) had died after 7 years of follow-up. Death certificates were obtained for 96.2% of participants known to have died. At the end of follow-up, 897 colon cancer deaths were observed in a cohort of 422,373 postmenopausal women who were cancer free at study entry. Cox proportional hazards modeling was used to compute rate ratios (RRs) and to adjust for other potential risk factors. The likelihood ratio test (two-sided) was used to determine the statistical significance of the interaction terms.Results: Ever use of ERT was associated with significantly decreased risk of fatal colon cancer (RR = 0.71; 95% confidence interval [CI] = 0.61-0.83). The reduction in risk was strongest among current users (RR = 0.55; 95% CI = 0.40-0.76), and there was a significant (P = .0001) trend of decreasing risk with increasing years of use among all users: Users of 1 year or less had an RR of 0.81 (95% CI = 0.63-1.03), while users of 11 years or more had an RR of 0.54 (95% CI = 0.39-0.76). These associations were not altered in multivariate analyses controlling for other risk factors.Conclusions: In our data, estrogen therapy, particularly recent and long-term use, was associated with a substantial decrease in risk of fatal colon cancer. These results were consistent with several published studies suggesting a protective role of exogenous estrogens in the development of colorectal cancer and merit further investigation. [ABSTRACT FROM AUTHOR]