Abstract PS3-09-02: Retrospective observational study of premenopausal ER+/HER2- patients in Greece with axillary tumor burden but low Oncotype DX® Recurrence Score who did not receive chemotherapy

Background The Oncotype DX® assay is a validated genomic test that aids in assessing the risk of distant recurrence and in predicting the potential benefit of adjuvant chemotherapy in patients with early-stage HR+, HER2- breast cancer. In premenopausal women with 1-3 positive lymph nodes (N1) and a Recurrence Score (RS) of 0-25, the RxPONDER trial demonstrated a 2.4% improvement in distant recurrence-free interval (DRFI) and a 4.9% improvement in invasive disease-free survival (IDFS) in pts receiving chemo-endocrine therapy compared to endocrine therapy alone. Pts who received only endocrine therapy had a DRFI of 93,9% and an IDFS of 89%. The aim of this observational study is to establish a registry and present data on DRFI and IDFS in premenopausal women with node-positive breast cancer and a low RS who, either by choice or due to comorbidities, did not receive chemotherapy and were treated with endocrine therapy alone (with/without ovarian function suppression - OFS). Methods We conducted a retrospective multicenter analysis across 9 institutions in Greece, focusing on pre- & peri-menopausal women diagnosed with ER+/HER2-, node-positive (pN1 or pN1mic) early breast cancer, who underwent Oncotype DX® testing between 01/2012-01/2025, had a low RS (0-25), and did not receive chemotherapy. Three additional pts with N0(i+) disease were not included in the cohort analysis. Results A total of 74 pts were included in the analysis. The median age of diagnosis was 47 (range 26-54) and the median RS was 12 (range 0-22). Cohort clinical data are summarized below. With a median follow-up of 4.8 years (range: 1-150 months), one patient developed a distant recurrence in the lung (T1, N1mic, G3, no OFS, RS 17), while another was diagnosed with contralateral breast cancer (T1, N1, G2, with OFS, RS 15). The estimated 5-year DRFI and IDFS were 98.6% (95% CI, 92.5%-99.9%) and 97.3% (95% CI, 90.7%-99.5%), respectively. Among the three N0(i+)pts, no recurrences were observed during a mean follow-up of 3.4 years. Conclusion While the RxPONDER trial demonstrated a modest benefit from the addition of chemotherapy in premenopausal node positive pts independently of the RS, these real-world data suggest that selected pts may achieve favorable outcomes with endocrine therapy alone. A substantial proportion of pts received OFS (52.7%), with nearly half having N1mic disease (44.6%) and most presenting with T1 tumors (81.1%), suggesting a biologically distinct subgroup with potentially different treatment needs. This highlights the potential of individualized treatment planning using Oncotype DX in pre-/peri-menopausal pts with limited axillary tumor burden. Further studies with larger patient cohorts and longer follow-up are warranted to better define outcomes and optimize treatment strategies in this subgroup. Citation Format: L. Papadopoulos, C. Markopoulos, K. Papazisis, F. Zagouri, S. Triantafyllidou, A. Tsiftsoglou, A. Zavos, A. Koumarianou, M. Kontos, A. Fokianou, P. Ntasiou, P. Kalogerakos, S. D. Eleftheriadis, F. Fostira, C. Iosifidou, C. Stefanou, D. Maniatis, S. Filippidou, R. Alevizou, A. Papadopoulou, G. Kapetsis, S. Giannoulakis, D. Grigoriadis, G. Xepapadakis. Retrospective observational study of premenopausal ER+/HER2- patients in Greece with axillary tumor burden but low Oncotype DX® Recurrence Score who did not receive chemotherapy [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 PS3-09-02.