Abstract 2279: Burden of colorectal cancer attributable to lifestyle-related risk factors: a pooled study of seven Australian cohorts
Authors: Vajdic Claire M. , Arriaga Maria , Hull Peter , Canfell Karen , MacInnis Robert , Banks Emily , Giles Graham , Mitchell Paul , Cumming Robert , Adelstein Barbara-Ann , Byles Julie , Magliano Dianna J. , Shaw Jonathan , Taylor Anne , Price Kay , Hirani Vasant , Laaksonen Maarit A. 
Published: July 2017

Abstract
Aim: To quantify the burden of colorectal cancer in Australia avoidable by modifications to established lifestyle-related risk factors: smoking, excess body weight, excessive red and processed meat consumption, excessive alcohol consumption and physical inactivity.
Methods: Data on exposure to lifestyle-related risk factors from seven Australian cohort studies (N = 367,772) were harmonized and pooled. The cohorts were linked to the Australian Cancer Database and National Death Index to identify incident cancers and deaths. The strength of the exposure-cancer and exposure-death associations were estimated using a proportional hazards model, adjusting for age, sex and the other lifestyle exposures. Age- and sex-specific exposure prevalence was estimated from the Australian National Health Survey (NHS) 2011-2012 or from the latest 45 and Up cohort study when not available in the NHS. These estimates were then combined to calculate the Population Attributable Fractions (PAFs), i.e. fractions of cancer attributable to the lifestyle-related risk factors, and their 95% confidence intervals (CIs) using an advanced method accounting for competing risk of death.
Results: During the first 10-years follow-up, 3,498 incident colorectal cancers and 20,135 deaths were ascertained as first events. Current or former smoking explained 9% (CI = 5-13%), BMI ≥ 25 kg/m2 9% (CI = 4-14%), red or processed meat consumption 3 or more times/week 6% (CI = 3-8%), and drinking more than 2 alcoholic drinks/day 4% (CI = 2-6%) of the colorectal cancer burden. PAF results for physical inactivity were not significant. The contribution of each factor was more pronounced in men than in women, with most of the burden attributable to excess weight in men (PAF = 15%, CI = 7-22%) and smoking in women (PAF = 7%, CI = 3-12%). Jointly the four significant lifestyle-related risk factors were responsible for 25% (CI = 19-30%) of the colorectal cancer burden, 33% (CI = 25-40%) in men and 15% (CI =7-23%) in women. Given the projected Australian incidence rates, this translates to 49,000 avoidable colorectal cancer cases, 35,000 in men and 14,000 in women, over the next 10 years.
Conclusions: These first Australian and international colorectal cancer PAF estimates based on cohort studies and accounting for competing risk of death show that several modifiable risk factors contribute to the burden of colorectal cancer and their ranking differs by sex. Further analyses may identify subpopulations that would benefit from targeted intervention activities. Due to the high incidence of colorectal cancer, these PAF estimates translate into a significant number of avoidable cases.
Citation Format: Claire M. Vajdic, Maria Arriaga, Peter Hull, Karen Canfell, Robert MacInnis, Emily Banks, Graham Giles, Paul Mitchell, Robert Cumming, Barbara-Ann Adelstein, Julie Byles, Dianna J. Magliano, Jonathan Shaw, Anne Taylor, Kay Price, Vasant Hirani, Maarit A. Laaksonen. Burden of colorectal cancer attributable to lifestyle-related risk factors: a pooled study of seven Australian cohorts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2279. doi:10.1158/1538-7445.AM2017-2279