Hypothetical Interventions on Diet Quality and Lifestyle Factors to Improve Breast Cancer Survival: The Pathways Study

Abstract Background: The number of breast cancer survivors is increasing, yet evidence to inform dietary and lifestyle guidelines is limited. Methods: This analysis included 3,658 participants from the Pathways Study, a prospective cohort of women diagnosed with invasive breast cancer. A healthy plant-based dietary index score (hPDI), an American Cancer Society (ACS) nutrition guidelines score, a 2015 Healthy Eating Index score (HEI), hours per week of moderate to vigorous physical activity (PA), and lifetime cumulative pack-years of cigarette smoking (SM) were each measured at diagnosis, 6, 24, and 72 months. Using g-computation, 5- and 10-year risk ratios (RR), risk differences, and 95% confidence intervals (CI) for all-cause mortality under hypothetical interventions on diet quality, PA, and SM, compared with the natural course (no intervention) were calculated. Results: Hypothetical moderate to extreme interventions on hPDI, ACS, and HEI, each in combination with PA and SM, showed 11% to 56%, 9% to 38%, and 9% to 49% decreases in 5-year risks of all-cause mortality compared with no intervention, respectively [(hPDI: RRmoderate = 0.89, 95% CI: 0.82–0.94; RRextreme = 0.44, 95% CI: 0.26–0.67), (ACS: RRmoderate = 0.91, 95% CI: 0.85–0.96; RRextreme = 0.62, 95% CI: 0.43–0.82), (HEI: RRmoderate = 0.91, 95% CI: 0.84–0.95; RRextreme = 0.51, 95% CI: 0.33–0.72)]. While 10-year relative risks were slightly attenuated, absolute risk reductions were more pronounced. Conclusions: Interventions to improve diet quality, increase PA, or reduce SM at the time of diagnosis may improve survival among breast cancer survivors. Impact: We estimate that over 10% of deaths could be delayed by even moderate adoption of these behaviors.