Regional nodal irradiation in pT1-2N1 breast cancer patients treated with breast-conserving surgery and whole breast irradiation

Purpose: To evaluate the necessity of regional nodal irradiation (RNI) for pT1-2N1 breast cancer patients treated with breast-conserving surgery and radiotherapy, we compared clinical outcomes of patients treated with and without RNI. Materials and Methods: We retrospectively analyzed the data of 214 pT1-2N1 breast cancer patients treated with breast-conserving surgery and whole breast irradiation from 2007-2016. There were 142 (66.4%), 51 (23.85%), and 21 (9.8%) patients with one, two, and three positive lymph nodes, respectively. Thirty-six patients (16.8%) underwent RNI. Adjuvant chemotherapy, endocrine therapy, and anti-HER2 therapy were given to 91.6%, 79.0%, and 15.0% patients, respectively. The most common chemotherapy regimen was anthracycline + cyclophosphamide, followed by taxane (76.5%). The median follow-up was 64 months (range, 6 to 147 months). Patients were propensity matched 1:2 into RNI and no-RNI groups. Results: Two patients experienced locoregional recurrences simultaneously with distant metastases, ten patients developed distant metastases, and one patient died. Before matching, the 5-year actuarial locoregional control (LRC), distant metastasis-free survival (DMFS), and overall survival (OS) rates in the RNI and no-RNI groups were 100.0% and 99.4% (p = 0.629), 94.1% and 96.0% (p = 0.676), and 100.0% and 99.4% (p = 0.658), respectively. After matching, the 5-year LRC, DMFS, and OS were 98.3% and 100.0% (p = 0.455), 96.6% and 93.9% (p = 0.557), and 100.0% and 100.0% (p > 0.999) in the RNI and no-RNI groups, respectively. No clinicopathologic or treatment-related factors were significantly associated with LRC, DMFS, or OS. Conclusion: Adding RNI did not show superior LRC, DMFS, or OS in pT1-2N1 breast cancer patients.