Abstract 1374: Adherence to the EAT-Lancet reference diet in adolescence and risk of invasive breast cancer among US women.

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Abstract In 2019, the EAT-Lancet Commission recommended a dietary pattern that is both good for human health and environmentally sustainable. The EAT-Lancet reference diet emphasizes high consumption of vegetables, fruits, whole grains, legumes, nuts, and unsaturated oils, low to moderate intake of seafood and poultry, and no to low intake of red meat, processed meat, added sugar, added saturated fat, refined grains, and starchy vegetables. The Planetary Health Dietary Index (PHDI) was subsequently developed to quantify adherence to this reference diet. Adolescence is marked by rapid breast tissue development and hormonal changes, presenting a susceptible window for breast carcinogenesis. Exposures during this period, including diet, could influence breast cancer risk.This study examines the association between the PHDI during adolescence and subsequent risk of invasive breast cancer in adulthood. We analyzed data from 47,355 women aged 33-52 years old in the Nurses’ Health Study II (NHSII) who recalled their adolescent diet using a food frequency questionnaire in 1998. PHDI scores were calculated to reflect adherence to the EAT-Lancet reference diet in adolescence. Participants were followed from 1998 until breast or other cancer diagnosis, death, loss to follow-up, or the end of 2019, whichever occurred first. Multivariable Cox Proportional Hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI).Over 896,674 person-years of follow-up, 1945 invasive breast cancer cases were documented, including 1245 estrogen receptor (ER) - positive and 233 ER-negative cases. Adolescent PHDI was not significantly associated with overall invasive breast cancer risk (HR for highest vs. lowest quartile = 0.89; 95% CI: 0.78, 1.02 ; p trend = 0.29), or with ER-positive breast cancer (HR = 1.00; 95% CI: 0.85, 1.18; p trend = 0.50). However, higher PHDI during adolescence was significantly associated with reduced risk of ER-negative breast cancer (HR = 0.69; 95% CI: 0.47, 1.00; p trend = 0.05), which was slightly attenuated after adjusting for weight change since age 18 (HR = 0.70; 95% CI: 0.48, 1.01; p trend = 0.06). The association between PHDI during adolescence and overall invasive breast cancer risk did not differ by menopausal status or by subgroups of body mass index at age 18.In conclusion, adherence to the EAT-Lancet reference diet during adolescence may reduce the risk of more aggressive breast cancer subtypes, particularly ER-negative cases, but not overall breast cancer. These findings highlight a dietary pattern that could be both health-promoting and environmentally sustainable during a key developmental period. Citation Format: Phuong Anh Le, Walter C. Willett, Bernard Rosner, Wendy Y. Chen, Michelle D. Holmes, Andrea Romanos-Nanclares, A. Heather Eliassen. Adherence to the EAT-Lancet reference diet in adolescence and risk of invasive breast cancer among US women [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1374.

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