Risk Factors to Identify the Indication for Regional Nodal Irradiation in T1-2N1M0 Breast Cancer: A Joint Analysis of 4243 Real-World Cases From Two Institutions

Abstract

To evaluate the role of regional nodal irradiation (RNI) in patients with T1-2N1M0 breast cancer and identify the subgroup that could benefit from RNI.A total of 4243 women with T1-2N1M0 breast cancer treated at two institutions were retrospectively reviewed. Among them, 3858 (90.9%) received mastectomy and 385 (9.1%) received breast-conserving surgery. A total of 932 (22.0%) patients received RNI. Locoregional recurrence (LRR), distant metastasis (DM), disease-free survival (DFS), and overall survival (OS) rates were calculated by the Kaplan-Meier method and compared by log-rank test. The association of risk factors with survival outcomes was evaluated using multivariable proportional hazards regression.At a median follow-up of 5.9 years (interquartile range: 4.1-8.4), the 5-year LRR, DM, DFS, and OS rates were 4.0% and 7.2% (P = 0.001), 13.2% and 10.6% (P = .465), 85.0% and 84.7% (P = .131), and 93.9% and 92.8% (P = 0.004) in the RNI and non-RNI groups, respectively. Multivariate analysis revealed that RNI was an independent prognostic factor for lower LRR (P = 0.001) and longer DFS (P = 0.013). Patients were stratified into low-, intermediate-, and high-risk groups based on eight non-therapeutic risk factors. RNI significantly decreased the 5-year LRR (2.2% vs. 7.0%, P = 0.001) and improved the 5-year DFS (88.8% vs. 84.9%, P = 0.015) and OS (95.8% vs. 93.9%, P = 0.010) in the intermediate-risk group. On the other hand, RNI only decreased LRR in high-risk group, and had no impact on low-risk group.T1-2N1M0 breast cancer is a heterogeneous disease. We found that RNI only improved survival in the intermediate-risk group. It might be omitted in low-risk patients, and the role of RNI in high-risk patients needs further study.