Abstract P5-12-01: The joint effect of modifiable risk factors on risk of invasive breast cancer among Canadian women

Background Although several studies have suggested that obesity and other modifiable factors influence breast carcinogenesis, there is limited evidence on the combined effect of these exposures on risk of breast cancer. Thus, to gain further insight into whether modifiable risk factors may operate collectively to alter risk of breast cancer, we assessed the association of a healthy lifestyle index (HLI) score (a combination of diet, physical activity, smoking, alcohol consumption and anthropometry) with risk of invasive breast cancer among women in the Canadian Study of Diet, Lifestyle, and Health (CSDLH). Method We performed a case-cohort study using a cohort of 39,532 female participants in the CSDLH who were recruited between 1995 and 1998. The study included an age-stratified subcohort of 3,027 women and 1,018 incident invasive breast cancer cases. Lifestyle and dietary information was collected at baseline using self-administered questionnaires. We estimated hazard ratios (HR) and 95 % confidence intervals (CI) for the association of the HLI score and the individual HLI components with risk of breast cancer using Cox proportional hazards regression modified for the case cohort design. Results: Every unit increase in the HLI score was associated with a 3% reduced risk of breast cancer (HR: 0.97; 95% CI: 0.95-1.00). When considering quintiles of the HLI score, those in the highest quintile had a 26% lower risk for breast cancer compared to those with HLI score in the lowest quintile (HR q5 vs q1 : 0.74; 95% CI: 0.59-0.93). In analyses stratified by menopausal status, there was a similar inverse association between the HLI score and risk of breast cancer among postmenopausal women (HR: 0.97; 95% CI: 0.94-1.00) and a tendency towards an inverse association among premenopausal women (HR per unit increase in the HLI score : 0.98; 95% CI: 0.95-1.01). Among the individual components of the HLI score, there was some suggestion of a reduction in risk of breast cancer in association with a relatively high physical activity level in the overall study population (HR q5 vs. q1 : 0.81: 95% CI: 0.63-1.04, p trend: 0.08), but consuming a healthy diet, smoking, having high alcohol consumption and being obese were not associated with altered risk of breast cancer. Conclusion: Our findings indicate that adherence to a healthy lifestyle may be associated with reduced risk of breast cancer. These findings suggest the need to further investigate how modifiable risk factors may act jointly to contribute to the development of breast cancer. Such knowledge may have important implications for the development of interventions designed to promote a healthy lifestyle to aid in the primary prevention of breast cancer. Citation Format: Arthur R, Kirsh V, Kreiger N, Rohan T. The joint effect of modifiable risk factors on risk of invasive breast cancer among Canadian women [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-12-01.