Abstract 6151: Relationship between polygenic risk score, lifestyle factors, and colorectal cancer risk
Authors: Huang Wen-Yi , Loftfield Erikka , Landy Rebecca , Wang Difei , Katki Hormuzd A. , Shi Jianxin , Wang Lingxiao , Machiela Mitchell J. , Freedman Neal D. , Berndt Sonja I. 
Published: March 2024

Abstract
Although heritable factors are estimated to explain up to 35% of colorectal cancers (CRC), most are diagnosed in people without a family history of CRC suggesting that inherited genetic variants, environmental factors, or a combination of both, contribute to CRC risk. We explored the relationship between a polygenic risk score (PRS) for CRC risk and lifestyle risk factors to understand whether individuals with higher genetic risk, who do not develop CRC, engage in healthier lifestyle behaviors, or conversely, whether those with lower genetic risk, who do develop CRC, engage in riskier behaviors in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial.
Using summary statistics obtained from a large independent GWAS meta-analysis of CRC by the GECCO consortium, we developed a genome-wide PRS for CRC using SBayesR and applied it to participants of European ancestry genotyped in the PLCO Trial (n=74,396). For all subjects, we computed an environmental (E) score based on 19 lifestyle risk factors for CRC, a WCRF/AICR score that measured adherence to the 2018 Cancer Prevention recommendations, and a 2015 healthy eating index (HEI) with higher values indicating healthier lifestyle profiles. We used t-tests to evaluate differences in lifestyle scores between CRC-free participants in the highest quartile of PRS and incident CRC cases in the lowest quartile of PRS. To examine the correlations between the PRS and lifestyle scores, we performed multivariable linear regression models regressing PRS on each lifestyle score. We used multivariable Cox hazards regression models to compute hazard ratios and 95% confidence intervals for CRC risk; multiplicative interactions between PRS and lifestyle scores were evaluated using the Wald test for the interaction terms.
During the 15 years follow-up period, a total of 1,052 CRC cases were diagnosed. Individuals in the highest quartile of PRS who remained cancer-free were more likely to engage in healthier behaviors than those in the lowest quartile of PRS who were diagnosed with incident CRC (E-score: -0.01 vs. -0.18, WCRF/AICR score: -0.05 vs. -0.32, HEI score: 0.06 vs. -0.13); however, differences were not statistically significant (P value: 0.1 to 0.4). PRS and lifestyle scores were significantly (all P &lt;0.0001), albeit weakly (β: -0.02 to -0.03), associated among participants who remained CRC-free but not among CRC cases (P: 0.1 to 0.3). PRS-lifestyle score interactions were not statistically significant (P: 0.2 to 0.4).
Although the differences and multiplicative interaction models were not statistically significant, we found that individuals with a higher PRS who remained CRC-free were slightly more likely to engage in healthier behaviors than those at a lower genetic score who developed CRC. Additional studies with larger sample size are warranted to further explore the interplay between genetic risk and lifestyle factors related to CRC risk.
Citation Format: Wen-Yi Huang, Erikka Loftfield, Rebecca Landy, Difei Wang, Hormuzd A. Katki, Jianxin Shi, Lingxiao Wang, Mitchell J. Machiela, Neal D. Freedman, Sonja I. Berndt. Relationship between polygenic risk score, lifestyle factors, and colorectal cancer risk [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6151.