Modeling the prevention of colorectal cancer from the combined impact of host and behavioral risk factors

Purpose: This study investigated the utility of modeling modifiable lifestyle risk factors in addition to genetic variation in colorectal cancer (CRC) screening/prevention. Methods: We derived a polygenic risk score for CRC susceptibility variants in combination with the established nongenetic risk factors of inflammatory bowel disease (IBD), adiposity, alcohol, red meat, fruit, vegetables, smoking, physical activity, and aspirin. We used the 37 known risk variants and 50 and 100% of all risk variants as calculated from a heritability estimate. We derived absolute risk from UK population age structure, incidence, and mortality rate data. Results: Taking into account all risk factors (known variants), 42.2% of 55-to 59-year-old men with CRC have a risk at least as high as that of an average 60-year-old, the minimum eligible age for the UK NHS National Bowel Cancer Screening Program. If the male population is stratified by known variants and IBD status, then risk-difference estimates imply that for 10,000 50-year-old men in the 99th percentile, 760 cases could be prevented over a 25-year period through the modifiable risk factors, but in the lowest percentile, only 90 could be prevented. Conclusion: CRC screening and prevention centered on modifiable risk factors could be optimized if targeted at individuals at higher polygenic risk.