Association between colorectal cancer, cigarette smoking, second-hand smoke exposure, and age at diagnosis.

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Objective: To examine the effect of cigarette smoking and second-hand smoke (SHS) exposure on age at diagnosis among colorectal cancer patients. Methods: Patients who were diagnosed with primary, incident colorectal cancer at Roswell Park Cancer Institute between 1957 and 1997 and completed a detailed epidemiological questionnaire were eligible for this case-only analysis. Approximately 3,539 colorectal cancer cases were classified by their self-reported cigarette smoking and SHS exposure status. Cigarette smoking and second-hand smoke exposures were the main independent variables, age at diagnosis was the outcome, and covariates included year of diagnosis, gender, and alcohol use (never or ever). Retsults: Active smoking was associated with a younger age at onset of colorectal cancer. Current smokers were diagnosed 6.8 years (p<0.001) prior to those who never smoked, while former smokers who recently quit (within the past 5 years prior to interview) were diagnosed 4.3 years before never smokers (p<0.001). Similar results were observed for other measures of active smoking such as amount smoked and pack years. A dose-response was also observed, where increased active smoking was associated with a younger age at diagnosis. SHS exposure among never smokers was also associated with an earlier age at diagnosis. Never smokers who were currently exposed to SHS at the time of diagnosis were diagnosed 2.5 (p=0.14) years earlier, while those who only had past SHS exposure were diagnosed 8.6 (p<0.001) years before those not exposed to SHS. Those exposed to both current and past SHS were diagnosed 11.6 (p<0.001) years prior to never smokers not exposed to SHS. Conclusions: Both cigarette smokers and never smokers exposed to SHS were diagnosed with colorectal cancer at a significantly younger age compared to their unexposed counterparts. If the results are confirmed, this could have implications for colorectal cancer screening, smoking cessation advice, and smokefree policies.