SMOKING AND COLORECTAL-CANCER - A 20-YEAR FOLLOW-UP-STUDY OF SWEDISH CONSTRUCTION WORKERS

Background: Although cigarette smoking has consistently been shown to be positively related to the risk of adenomatous polyp development (be nign neoplastic growth of epithelial tissue in the colon), most studie s of cigarette smoking and the risk of colorectal cancer have been neg ative, However, in two large prospective studies in women and men, a s tatistically significant association between cigarette smoking and an increased risk of colorectal cancer was found, but only after more tha n 35 years of smoking, Purpose: To shed further light on the alleged r elationship between long-term smoking and colorectal cancer risk, we p erformed a retrospective cohort study among Swedish construction worke rs, with many long-term smokers, complete long-term follow-up, and a l arge number of observed cases, Methods: We analyzed the association of smoking with colon cancer and with rectal cancer, using data on a coh ort of approximately 135 000 male construction workers, High-quality e xposure information was collected with the use of a comprehensive ques tionnaire filled out at the time of enrollment in the cohort, from 197 1 through 1975, Complete follow-up was achieved through 1991 and the s ubjects were observed for an average of 17.6 years, thereby contributi ng approximately 2 375 000 person-years of folllow-up, We calculated a ge-adjusted rate ratios (RRs) with the use of Poisson-based multiplica tive multivariate models followed by further multivariate modeling tha t adjusted for either variables. Results: A total of 713 incident colo n cancers and 505 rectal cancers were observed, There was no statistic ally significant association between current smoking status, number of cigarettes smoked or number of years smoking, and risk of colorectal cancer, The age-adjusted RRs were 0.98 (95% confidence interval [CI] = 0.82-1.17) and 1.16 (95% CI 0.94-1.44) for colon and rectal cancers, respectively, among current smokers, and 1.07 (95% CI = 0.63-1.82) and 1,08 (95% CI = 0.58-2.033 among smokers of 25 or more cigarettes per day, relative to nonsmokers, Among smokers for more than 30 years at t he start of follow-up, the age-adjusted RRs were 1.03 (95% CI = 0.85-1 .35) and 1.21 (95% CE = 0.96-1.53) for colon and rectal cancers, respe ctively; relative to nonsmokers, Heavy smokers of cigars and pipes had a statistically nonsignificant tendency toward excess risk for colon cancer, but there was no clear dose-risk trend, Conclusion: Our large cohort study did not indicate any excess risk of colon cancer in males who were long-term heavy smokers and weak support for an Our the majo rity of previous reports, The reasons for the discrepancies in compari son with recent U.S. data have yet to be identified.