Abstract PS3-09-30: Real-World Outcomes of Neoadjuvant Chemotherapy vs Endocrine Therapy in ER+/HER2− and HER2-Low Early Breast Cancer: A Single-Institution Retrospective Study

Abstract Background Neoadjuvant chemotherapy (NAC) and endocrine therapy (NET) are both used in ER+/HER2− or HER2-low breast cancer, yet comparative real-world data remain limited. This study aimed to evaluate treatment patterns, pathological response, and clinical outcomes between NAC and NET in this setting. Methods We retrospectively analyzed 211 ER+/HER2− or HER2-low early breast cancer patients who received neoadjuvant systemic therapy at King Fahad Medical City. Patients were grouped by treatment type: NAC (n=169) and NET (n=42). Luminal subtypes were defined by histologic grade and Ki-67 index. Key outcomes included pathologic complete response (pCR; defined as ypT0/is and ypN0), nodal and tumor downstaging, breast-conserving surgery (BCS), and recurrence-free survival (RFS). Results The NAC and NET groups represented distinct clinical populations. Patients receiving NET were older (median 66.5 vs 47.0 years), more often postmenopausal (90.5% vs 50.9%), and had a higher burden of comorbidities and ECOG 2+ status. NAC was more commonly used in patients with Grade 3 tumors, high Ki-67, and Luminal B subtype. pCR was observed in 9.5% of NAC and 4.8% of NET patients. Nodal downstaging occurred in 16.6% of NAC patients and 7.1% of NET patients. Tumor downstaging was observed in 68.3% of NAC patients and 74.2% of NET patients who underwent surgery. BCS was achieved in 17.8% of NAC patients and 9.5% of NET patients. Distant recurrence was reported in 6.5% of NAC and 2.4% of NET patients. Among those who recurred, the median RFS was 20.6 months for NAC and 13.3 months for NET. Conclusions In this real-world study, NAC was favored in younger, fitter patients with aggressive tumor features, while NET was reserved for older patients or those with more favorable disease biology. pCR and nodal response rates were higher in the NAC group, but treatment selection reflected inherent baseline differences. Tumor downstaging and low recurrence rates were observed with both strategies. Citation Format: A. A. Almazyad, M. Rudainee, M. H. Alharbi, A. A. Alwohaibi, N. Algazlan, A. R. altamimi, F. H. Faqihi, A. K. Altwairgi. Real-World Outcomes of Neoadjuvant Chemotherapy vs Endocrine Therapy in ER+/HER2− and HER2-Low Early Breast Cancer: A Single-Institution Retrospective Study 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 PS3-09-30.