Main Session
Sep
29
SS 40 - Evolving Paradigms in High-Risk Breast Cancer: Optimization and Integration of Treatment Modalities Across the Disease Continuum
320 - Simultaneous Integrated Boost in Hypofractionated Regional Lymph Node Irradiotherapy for cN3 Breast Cancer: Preliminary Report of a Prospective Phase 2 Single-Arm Trial
Presenter(s)
Yutong Tan, MD - National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Shenzhen, Guangdong
Y. Tan1, X. Su1, W. Zhang1, L. Feng1, J. Lei1, L. N. Chen1, N. Hu1, T. Lei1, Q. Xiao1, and J. Jin2; 1Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, 2Department of Radiation Oncology,National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China
Purpose/Objective(s):
While multiple phase III studies have established the efficacy and safety of hypofractionated radiotherapy after breast cancer surgery, the role of a simultaneous integrated boost to involved regional lymph nodes (cN3) in this setting remains undefined. This study reports preliminary outcomes from a prospective phase 2 trial evaluating this approach.Materials/Methods:
The trial enrolled women aged 18–75 years with newly diagnosed M0 breast cancer and cN3 stage disease confirmed by imaging or pathology. Patients who had not undergone internal mammary (IMN) or supraclavicular/infraclavicular (SC/IC) lymph node dissection were eligible. The primary endpoint was the incidence of adverse events. Postoperative radiation therapy was delivered as follows: (1) Chest wall/whole breast + regional nodal irradiation (RNI): 43.5 Gy in 15 fractions; (2) Boost to IMN or SC/IC positive lymph nodes: A. For patients achieving a complete response (CR) after systemic therapy: 49.5 Gy in 15 fractions;B. For those not achieving CR: 52.5 Gy in 15 fractions.Results:
Between August 2022 and August 2025, 43 patients were enrolled, with a median age of 43 years (range 22–73). Disease stages were cN3a in 16 patients (37.2%), cN3b in 6 (13.9%), and cN3c in 21 (48.8%). Neoadjuvant chemotherapy was administered to 38 patients (88.4%), of whom 9 achieved pathological complete response (pCR). The remaining 5 patients (11.6%) received adjuvant chemotherapy. Ten patients (23.3%) underwent breast-conserving surgery, and 33 (76.7%) underwent modified radical mastectomy, including 9 (20.9%) with breast reconstruction.As of January 31, 2026, all patients were alive. At a median follow-up of 26.8 months, one patient developed supraclavicular and internal mammary lymph node (IMN) recurrence with concurrent distant metastasis at 16.8 months post-radiotherapy; this patient had achieved pCR after neoadjuvant chemotherapy and modified radical mastectomy. Another patient experienced distant metastasis alone at 11.9 months.Grade = 2 adverse events were observed in 11 patients (25.5%), with no grade = 3 adverse events reported. The most common acute toxicity was dermatitis, with grade 2 dermatitis occurring in 8 patients (18.6%). Mild upper limb lymphedema and shoulder dysfunction were noted in 1 patient (2.3%) and 2 patients (4.6%), respectively.Conclusion:
This preliminary analysis suggests that hypofractionated regional lymph node irradiotherapy with simultaneous integrated boost to involved lymph nodes is a feasible and safe treatment strategy for patients with cN3 breast cancer, demonstrating promising early local control with a manageable toxicity profile.