Abstract PD8-03: Impact of Obesity in Premenopausal Women with Early-Stage HR+/HER2- Breast Cancer Treated With Adjuvant Endocrine Therapy

Abstract Background: Hormone receptor positive (HR+)/Human Epidermal Growth Factor Receptor 2 negative (HER2–) breast cancer is the most common subtype of breast cancer and is primarily treated with endocrine therapy (ET), including tamoxifen (tam) alone or ovarian function suppression (OFS) with tam or aromatase inhibitors (AI). Body mass index (BMI) can influence the effectiveness of ET; however, the impact of BMI on outcomes in premenopausal women remains unclear. Previous studies in postmenopausal women have shown worse outcomes among obese women receiving ET. Given the rise in obesity and limited literature focused on premenopausal patients, it is essential to gain a better understanding of how BMI affects ET outcomes. Methods: We analyzed the medical records of premenopausal women (defined as age 50) with Stage 1-3 HR+/HER2– breast cancer from January 2012 to December 2023. We collected demographic, clinicopathologic characteristics, and treatment information. Patients with non-invasive breast cancer, those who did not begin ET, and those who received an AI alone were excluded. We examined recurrence and survival outcomes by BMI and ET type, controlling for age, tumor grade, and stage. Results: 723 women with Stage 1-3 HR+/HER2- breast cancer treated with ET were identified. Of these, 345 were characterized as normal weight (BMI ≤ 24.9), 210 were overweight (BMI 25.0-29.9), and 168 were obese/severely obese (BMI ≥ 30.0). There was a significant difference in BMI among racial groups, with Black and Hispanic patients diagnosed with breast cancer being more likely to be obese/severely obese than White or Asian/Pacific Islander (API) women. Women with higher BMIs were also more likely to be diagnosed with larger tumors (≥ 3.0 cm), but there was no significant interaction between BMI and clinical stage, node positivity, or grade. Of the 723 total patients treated with ET, 185 (25.6%) received OFS with either Tam or an AI. 538 (74.4%) of patients were treated with Tam alone. Multivariable analysis controlling for age, grade, and stage did not show that increasing BMI was associated with Tam alone use (OR 0.99 (0.96-1.01), p=0.2997). At a median follow-up of 66 months, 64 patients were found to have a breast cancer recurrence: 32 recurrences occurred in women with normal weight, 17 recurrences occurred in those who were overweight, and 15 recurrences occurred in those who were obese/severely obese. 5-year survival rates were 94.6% in the obese/severely obese group; 95.1% in the overweight group and 98.1% in the normal weight group (p=0.7027). Conclusions In contrast to currently reported data in postmenopausal women, we did not find that premenopausal women with early-stage HR+/HER2– breast cancer and higher BMIs were at increased risk of recurrence or worse survival but longer term follow up is needed. Citation Format: P. Saha, O. Israel, C. Sanchez, L. Eldridge, K. Kuchta, K. A. Yao. Impact of Obesity in Premenopausal Women with Early-Stage HR+/HER2- Breast Cancer Treated With Adjuvant Endocrine Therapy abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PD8-03.