Abstract PS3-07-27: Identifying Premenopausal Patients with Early-Stage Hormone Receptor-Positive Node-Negative Breast Cancer at Minimal Risk of Distant Recurrence by Breast Cancer Index

Abstract Background: Adjuvant endocrine therapy for 5 years with ovarian function suppression (OFS) is recommended for premenopausal breast cancer patients with endocrine-sensitive tumors at high enough risk of recurrence, e.g. younger age, high grade tumor or nodal involvement. Genomic risk assessment may help to personalize OFS-based treatment selection. The Breast Cancer Index (BCI) test was previously confirmed as prognostic in premenopausal patients in the SOFT and TEXT trials [1]. For hormone receptor-positive (HR+), node-negative (N0) breast cancers, an adjusted BCI model with an additional cutpoint was recently developed that re-stratified postmenopausal patients with BCI low risk breast cancer into BCI minimal or low risk; where the new minimal risk group had a 10-year risk of distant recurrence of <5% [2]. Here, we evaluated the prognostic performance of the adjusted BCI model in premenopausal patients with HR+ N0 breast cancer in the SOFT and TEXT trials; the median follow-up was 12 and 13 years, respectively. Methods: The analysis included 1110 N0 patients from SOFT (N = 383 assigned tamoxifen; N = 727 assigned exemestane+OFS or tamoxifen+OFS), of whom 70 experienced DR; and 915 N0 patients from TEXT (assigned exemestane+OFS or tamoxifen+OFS), of whom 64 had DR. The new BCI cutpoint, along with the current cutpoints, was used to re-stratify N0 patients as minimal or low risk, with those in intermediate or high risk groups remaining as previously classified. The primary endpoint was distant recurrence-free interval (DRFI). 10-year DR was reported as one minus Kaplan-Meier estimate of DRFI with pointwise 95% confidence intervals (CI). Results: The adjusted BCI model re-classified 18% and 20% of N0 patients in SOFT and TEXT into the BCI minimal risk group; 43% and 38% remained classified in the low-risk group, respectively. Of those with minimal-risk BCI tumors in SOFT, 86% were ≤2cm and 51% were grade 1 tumors, 85% did not receive chemotherapy, 62% were age ≥45y. Of those with minimal-risk BCI tumors in TEXT, 80% were ≤2cm and 35% were grade 1 tumors, 73% did not receive chemotherapy, 51% were age ≥45y. 10-yr DR estimates are tabulated. Conclusions: This study confirms the prognostic ability of the adjusted BCI model to identify a subset of premenopausal patients whose estimated 10-year risk of DR was <5%. These findings provide clinicians and premenopausal patients with additional information for discussions about potential benefits and side effects of adjuvant endocrine therapy regimens. References: [1] (O’Regan et al; PMID 39145953). [2] (Jilderda et al; PMID 40145943) Citation Format: R. O'Regan, Y. Ren, Y. Zhang, G. F. Fleming, P. A. Francis, O. Pagani, B. A. Walley, R. Kammler, P. Dell’Orto, G. Viale, S. Loi, M. Colleoni, K. Treuner, M. Regan. Identifying Premenopausal Patients with Early-Stage Hormone Receptor-Positive Node-Negative Breast Cancer at Minimal Risk of Distant Recurrence by Breast Cancer Index [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 PS3-07-27.