Abstract 4944: Role of a planetary health diet in survival following breast cancer diagnosis

Abstract Introduction: Whilst the current trend recommendation for breast cancer survivors to follow a healthy plant-centric diet seems prudent, evidence supporting this remains limited. Furthermore, diets that address both human health and environmental sustainability remain a research priority, and the EAT-Lancet Commission's 2019 "Planetary Health Diet" has offered a framework for this approach. Our study aimed to investigate whether a Planetary Health Diet Index (PHDI), quantifying adherence to these targets, is associated with overall and breast cancer-specific mortality. Methods: For 7, 639 women with stage I-III breast cancer from the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII), we calculated the cumulative average PHDI, using repeated measures of post-diagnostic diet assessed by food frequency questionnaires (FFQ). The PHDI index included a variety of high-quality plant-based foods (whole grains, fruits, vegetables, nuts and legumes) and low amounts of animal-based foods, refined grains, added sugars, and unhealthy fats. Deaths were ascertained by report from family members or by searching the National Death Index. Hazard ratios (HRs) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models and adjusted for multiple time-varying and fixed-time covariates (measured prior to or at the time of diagnosis) and clinical factors. Results: Participants were followed up for a median of 12 years after breast cancer diagnosis. We documented 2, 983 deaths, including 788 due to breast cancer. In the multivariable-adjusted model, we observed a statistically significant inverse association for cumulatively averaged post-diagnosis PHDI and all-cause mortality (HRQ5vs.Q1 0.85 [0.73, 0.99], p-trend <0.01), but not breast cancer specific mortality. Findings for overall mortality were similar for PHDI measured at other timings/settings, including the first post-diagnosis dietary assessment (HRQ5vs.Q1 0.88 [0.76, 1.01], p-trend <0.01). Conclusions: High adherence to a diet consistent with both human and planetary health after a breast cancer diagnosis is associated with lower risk of all-cause, but not breast cancer-specific, mortality. As the number of breast cancer survivors grows and environmental sustainability becomes more urgent, strategies to reduce mortality should focus on the win-win benefits of dietary changes for both population and planetary health. Citation Format: Andrea Romanos-Nanclares, Michelle D. Holmes, Wendy Y. Chen, Walter C. Willett, Bernard A. Rosner, A. Heather Eliassen. Role of a planetary health diet in survival following breast cancer diagnosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4944.