The risk of developing rectal cancer due to active cigarette smoking and passive smoke exposure

Purpose The objective of this study was to examine whether active smoking and passive smoke exposure contributes to rectal cancer risk. Methods We prospectively studied smoking status in relation to the incidence of rectal cancer in two cohorts established in Washington County, MD. Measurement of exposure to passive smoke was based on residing with cigarette smokers. Two cohorts were followed up from 1963–1978 (N = 45,749) and from 1975–1994 (N = 48,152). The Washington County Cancer Registry was used to ascertain diagnoses of rectal cancer occurring in these cohorts. Poisson regression models were fitted to estimate age- and multivariate-adjusted rate ratios (RR) associated with active and passive smoking status, in comparison to the referent category of never smokers not exposed to household passive smoke. Results Among current active smoking men, the adjusted RRs for rectal cancer were 3.0 (95% CI 1.2–7.8) in the 1963 cohort and 1.8 (95% CI 0.9–3.7) in the 1975 cohort. The risk of rectal cancer in the 1963 cohort showed less evidence of being associated with tobacco exposure in women, with current active smoking not significantly associated with rectal cancer in the 1963 (RR 0.9; 95% CI 0.5–1.8) or 1975 (RR 1.6; 95% CI 0.9–3.8) cohorts. Passive smoke exposure was strongly associated with rectal cancer in men in the 1963 (RR 5.8; 95% CI 1.8–18.4) but not the 1975 (RR 1.1; 95% CI 0.2–5.0) cohort. In women, passive smoke exposure in nonsmokers was not associated with rectal cancer in either cohort. Discussion This study adds data from a prospective cohort study to previous evidence concerning the possible association between cigarette smoking and rectal cancer. Evidence linking active and passive smoke exposure to rectal cancer risk was observed, but it was limited to men, and even the associations among men were largely confined to the earlier 1963 cohort. As in our study, the overall evidence has hinted that cigarette smoke may be associated with rectal cancer, but has not been consistent. The index of suspicion thus remains high, pointing to the need for additional studies.