2746 - Clinical Outcomes after Post-Operative Radiotherapy for Breast Cancer Patients Presenting with Ipsilateral Supraclavicular Metastasis: Considerations on the Cranial Border of Irradiation Field

X. Wang¹, X. Zhang¹, L. Zhang¹, J. Meng¹, W. Shi¹, X. Chen¹, Z. Yang¹, X. Mei¹, X. Yu¹, Z. Zhang², Z. Shao³, X. Guo¹, and J. Ma¹; ¹Department of Radiation Oncology, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University; Shanghai Clinical Research Center for Radiation Oncology; Shanghai Key Laboratory of Radiation Oncology, Shanghai, China, ²Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China, ³Department of Breast Surgery, Precision Cancer Medicine Center, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China

Purpose/Objective(s): Ipsilateral supraclavicular lymph node (SCV LN) metastasis, classified as N3c in the 8^th AJCC clinical staging system, was considered potentially curable with multidisciplinary treatment. Among the treatment options, radiotherapy (RT) plays a crucial role in the local control of the SCV region. However, the optimal cranial border of irradiation field remains controversial. Therefore, this study aims to report the survival outcomes and discuss the reasonable cranial border of the irradiation field for patients diagnosed with ipsilateral SCV metastasis but without distant metastasis in the new era of systemic treatment. Materials/

Methods: A total of 268 patients who were staged as N3c and underwent radical surgery and RT were enrolled in the study between July 2016 and January 2022. Patient characteristics, treatments, imaging data, and RT plan were reviewed. The endpoints included local-regional recurrence-free survival (LRRFS), SCV recurrence-free survival (SRFS), distant metastasis-free survival (DMFS), relapse-free survival (RFS), and overall survival (OS). Survival rates were calculated using the Kaplan-Meier method. Univariate and multivariate analyses were conducted using the Cox regression model to identify recurrence risk factors.
Results: During a median follow-up of 35 months (range, 1-84 months), 17 patients (6.3%) developed local-regional recurrence (LRR) as the first recurrence event, with 13 having concomitant distant-metastasis (DM); 53 patients (19.8%) had DM alone. The 3-year rates of LRRFS, SRF, DMFS, RFS, and OS were 92.7%, 95.0%, 75.1%, 73.6%, and 89.0%, respectively. 89.2% of patients received RT with the cranial border at the top of hyoid bone, and 95.1% of patients received a boost not exceeding the level of cricoid cartilage. A total of 11 patients (4.1%) developed ipsilateral SCV metastasis and 3 patients (1.1%) experienced cervical lymph nodes metastasis. Neoadjuvant systemic therapy (NST) was administered to 234 patients (87.3%). In the multivariate analysis, non-ypN0 and triple-negative subtype were predictors of worse SRFS; these factors along with cT4, were associated with worse RFS in NST subgroup.
Conclusion: In the era of modern systemic therapy, radical RT with cranial border of irradiation field at the hyoid bone level after breast and axilla surgery could lead to satisfactory regional control and long-term survival for patients with ipsilateral SCV metastasis at diagnosis. Tailored based on recurrence risk factors, adaptive RT could be considered to optimize therapeutic outcomes in future prospective trials.