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

The number of breast cancer survivors is increasing, yet evidence to inform dietary and lifestyle guidelines is limited. 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. 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. Interventions to improve diet quality, increase PA, or reduce SM at the time of diagnosis may improve survival among breast cancer survivors. We estimate that over 10% of deaths could be delayed by even moderate adoption of these behaviors.