Multivariable associations of demographic, clinical and lifestyle factors with subsite-specific risk of colorectal cancer according to age at diagnosis (Younger-onset CRC: diagnosed at age of <60 years; older-onset CRC: diagnosed at age of ≥60 years) in the NHS, NHS2, and HPFS.
Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using age- and cohort-stratified Cox proportional hazards model with further adjustment for race, height (continuous), family history of colorectal cancer (yes or no), history of lower gastrointestinal endoscopic screening (yes or no), body mass index (continuous), pack-years of smoking (continuous), physical activity (continuous), alcohol intake (continuous), and regular aspirin use (yes or no). When age and sex are the main exposures, the model was only adjusted for each other of the two variables. P for heterogeneity was calculated between younger-onset CRC and older-onset CRC using the contrast test method. Abbreviations: BMI, body mass index; CRC, colorectal cancer; HPFS, the Health Professionals Follow-up Study; NHS, the Nurses’ Health Study.