S277
Clinical - Breast
ESTRO 2026
1 Radiation Oncology Department, Hacettepe University, Ankara, Turkey. 2 Medical Oncology Department, Hacettepe University, Ankara, Turkey. 3 Pathology Department, Hacettepe University, Ankara, Turkey Purpose/Objective: “HER2-low breast cancer” is defined as tumors exhibiting HER2 IHC scores of 1+ or 2+, without amplification in FISH. DESTINY-Breast04 trial has established the impact of trastuzumab deruxtecan on PFS and OS in metastatic patients with HER2-low tumors, establishing this molecular profile as a distinct entity [1]. In this study, we aimed to analyze and compare the clinicopathological features and survival outcomes of patients with locally advanced HER2-low and HER2-positive tumors. Material/Methods: We retrospectively evaluated 196 patients who underwent surgery and adjuvant RT after neoadjuvant chemotherapy (CT) between July 2000 and April 2024. RT fields included the whole breast or chest wall ± regional lymphatics. Kaplan–Meier curves were generated, and statistical analyses were performed using SPSS version 23.0 (SPSS, Chicago, IL). Results: All patients were female, and the median age was 48 years (24-74 years). A total of 108 patients were ER+ and 98 patients were PR+. HER2 analysis showed that 26 patients (13.3%) were HER2-low with IHC 1+, 15 patients (7.7%) were HER2-low with IHC 2+, and 155 patients (79.1%) were HER2-positive. Among the HER2- positive group, 72 patients (46.5%) had the HER2- enriched subtype, whereas 83 patients (53.5%) had the luminal B/HER2-positive subtype. The clinicopathological and treatment characteristics of the whole group were stratified by HER2 expression presented in Table 1.
metastatic TNBC treated with SG between August 2021 and October 2025 across multiple centers participating in the Central European Breast Cancer Collaboration (CEBCC), including Poland, the Czech Republic, and Slovakia. All patients received SG according to standard protocols. RT was administered in 69 patients (22.6%), including 8 who received SBRT (2.6%). Progression-free survival (PFS) was defined as the time from SG initiation to disease progression or death, and overall survival (OS) as the time from SG initiation to death or last follow-up. Survival was estimated using the Kaplan–Meier method, and between-group comparisons were performed using Fisher’s exact test. Statistical analyses were performed with Stata 19.5 (StataCorp LLC, College Station, TX, USA). Results: Both PFS and OS appeared longer in patients treated with SBRT compared to those receiving other RT regimens. Median PFS was 10.3 months with SBRT versus 3.1 months with other RT (p=0.3), with 6-month PFS rates of 51.4% (95%CI 11.8–81.3%) and 35.1% (95%CI 22.3–48.1%), respectively. Median OS was 14.5 months in the SBRT group versus 9.0 months in the other RT group, with corresponding 12-month OS rates of 71.4% (95%CI 25.8–92.0%) and 30.9% (95%CI 18.4–44.2%). Importantly, toxicity profiles were similar: no unexpected or increased adverse effects were observed from combining SBRT with SG Conclusion: SBRT appears to be a safe and feasible component of combined modality therapy in patients receiving sacituzumab govitecan for metastatic TNBC. The absence of excess toxicity and a potential trend toward improved outcomes suggest a synergistic benefit from integrating localized high-precision radiotherapy with ADC-based systemic therapy. However, SBRT remains substantially underused in this population despite its potential clinical advantages. Prospective studies with larger cohorts are warranted to validate these findings and to better define the optimal sequencing and patient selection for RT–ADC combinations. Keywords: Sacituzumab govitecan, multimodal therapy, ADC Treatment Outcomes in Patients with HER2-Low & Positive Breast Cancer Undergoing Neoadjuvant Systemic Therapy: Radiation Oncologists’ Perspective Melek Tugce Yilmaz 1 , Melis Gultekin 1 , Sepideh Mohammadipour 1 , Nihat Demir 1 , Sezin Yuce Sari 1 , Sercan Aksoy 2 , Kemal Kosemehmetoglu 3 , Gokhan Ozyigit 1 , Ferah Yildiz 1 Digital Poster 2444
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