SMOKING AND RISK OF COLORECTAL-CANCER

Tobacco smoking was studied in relation to colorectal cancer in 56 973 Finnish men and women initially free from cancer. Smoking status was determined by a health questionnaire. During a follow-up period of 28 years, from the baseline in 1966-72 to the end of 1994, 457 cases of c olorectal cancer occurred. There was no significant association betwee n baseline smoking status and colorectal cancer risk over the total fo llow-up period. The sex- and age-adjusted relative risk of colorectal cancer between smokers and non-smokers was 1.06 (95% confidence interv al 0.84-1.33). For follow-up periods of 11-20 years, however, the rela tive risk was 1.57 (95% confidence interval 1.09-2.24). In a subgroup in which smoking habits were assessed twice, the relative risk of colo rectal cancer among persistent smokers was 1.71 (95% confidence interv al 1.09-2.68) compared with others. The results of the present prospec tive study are consistent with the possibility that smoking increases the risk of colorectal cancer after a relatively long induction period . To clarify the role of smoking in colorectal cancer development, fur ther cohort studies are needed with long follow-up periods and allowin g for control of dietary and other potential confounding factors.