INCREASED RISK OF COLORECTAL-CANCER AMONG SMOKERS - RESULTS OF A 26-YEAR FOLLOW-UP OF US VETERANS AND A REVIEW

To clarify the relationship between tobacco use and risk of colorectal cancer, we evaluated a cohort of 248,046 American veterans followed p rospectively for 26 years. In comparison with veterans who had never u sed tobacco, the risk of death was significantly increased for colon c ancer and rectal cancer among current and former cigarette smokers and among pipe or cigar smokers, controlling for social class and occupat ional physical activity. Rectal-cancer risk was also significantly ele vated among users of chewing tobacco or snuff. For both sites, risk in creased significantly with pack-years, earlier age at first use, and n umber of cigarettes. These results reinforce 2 recent reports of the a ssociation of cigarette smoking and colorectal cancer in men and women . Inconsistencies in the findings of earlier epidemiologic studies app ear to be due in large part to differences in length of follow-up or i n choice of controls. Studies with at least 20 years of follow-up or p opulation-based controls have tended to find elevated risk with tobacc o smoking, while those with shorter follow-up or hospital controls hav e not. This, plus the strength and consistency of the association of s moking and colon polyps, suggest that smoking may primarily affect an early stage in the development of colon cancer. If this association is causal, tobacco use may be responsible for 16% of colon-cancer and 22 % of rectal-cancer deaths among these veterans. (C) 1995 Wiley-Liss, I nc.