ESTRO 2024 - Abstract Book

S529

Clinical - Breast

ESTRO 2024

Keywords: preoperative partial breast irradiation; MR-guided

References:

1. Vasmel JE, Charaghvandi RK, Houweling AC, et al. Tumor Response After Neoadjuvant Magnetic Resonance Guided Single Ablative Dose Partial Breast Irradiation. Int J Radiat Oncol Biol Phys 2020; 106(4): 821-9.

2. Civil YA, Jonker LW, Groot Koerkamp MPM, et al. Preoperative Partial Breast Irradiation in Patients with Low-Risk Breast Cancer: A Systematic Review of Literature. Annals of Surgical Oncology 2023.

991

Digital Poster

Exclusion of AXL1 from regional nodal irradiation in patients with breast cancer

Hwa Kyung Byun

Yongin Severance Hospital, Radiation Oncology, Seoul, Korea, Republic of

Purpose/Objective:

The optimal extent of regional nodal irradiation (RNI) in postoperative radiotherapy for breast cancer, specifically concerning axillary level 1 (AXL1), is uncertain. This study aimed to compare clinical outcomes between limited RNI, excluding AXL1, and extensive RNI, including the entire axilla, in patients with breast cancer.

Material/Methods:

A retrospective analysis included 1,780 women with non-metastatic unilateral breast cancer who underwent RNI between 2007 and 2018. Propensity score matching yielded a cohort of 1,020 patients. Non-inferiority of limited RNI compared to extensive RNI was assessed with a defined margin of ≤2% in the 5 -year axillary recurrence rate.

Results:

After a median follow-up of 67.9 months, the 5-year axillary recurrence rates were similar between extensive and limited RNI groups (1.2% vs. 1.6%; Plog-rank=0.790). Limited RNI demonstrated non-inferiority with a 0.4% difference (95% confidence interval, -1.1% – 1.9%; Pnon-inferiority=0.018). Disease-free survival (87.9% vs. 91.5%; Plog-rank=0.122) and overall survival (94.1% vs. 96.9%; Plog-rank=0.260) at 5 years were not significantly different between the extensive and limited RNI groups. Multivariable analysis revealed that lymphovascular invasion (hazard ratio [HR], 6.23; P=0.009) and negative hormone receptor status (HR, 10.46; P=0.003) were associated with a higher risk of axillary recurrence, while limited RNI showed no significant association (HR, 1.28; P=0.710).