Candidate Genetic Loci Modifying the Colorectal Cancer Risk Caused by Lifestyle Risk Factors.

Introduction: 65%-70% of colorectal cancer (CRC) cases are considered sporadic; they arise under the influence of environmental factors in individuals lacking a family history of CRC. Low-risk genetic variants are believed to contribute to CRC risk, in tandem with lifestyle factors.

Methods: Six hundred sixteen nonfamilial Swedish CRC cases with at least 1 of the following 5 risk factors: smoking, excessive alcohol consumption, physical inactivity, adherence to an unhealthy diet, and excess body weight were included in this study. A control group consisting of 1,642 healthy individuals was used. Cases and controls were genotyped from blood samples at the Centre for Inherited Disease Research at Johns Hopkins University within the Colorectal Transdisciplinary Study research collaboration, using the Illumina Infinium OncoArray-500 K BeadChip. Five separate genome-wide haplotype association analyses were performed, one for each risk factor. Logistic regression models were used to estimate associations between haplotypes (exposure) and CRC (outcome) in cases with lifestyle risk factors vs controls. Haplotypes with an odds ratio >1 were considered candidate risk markers, denoting an area of interest in the genome. A significance threshold of P < 5 × 10 -8 was used.

Results: We found 17 haplotype regions significantly associated with CRC in cases vs controls. Several regions included genes linked to inflammation and tumor promotion.

Discussion: We concluded that having certain genetic variants was associated with an increased risk of CRC compared with healthy controls among cases with known lifestyle risk factors. The interplay of lifestyle and genetic risk factors calls for further elucidation.