Feasibility of omitting regional nodal irradiation in cT1-2N1 breast cancer with ypN1 disease after neoadjuvant chemotherapy (KROG 21-06).

PURPOSE: To evaluate the effect of regional nodal irradiation (RNI) in breast cancer patients with 1-3 residual nodal metastases (ypN1) after neoadjuvant chemotherapy (NAC).

METHODS

We retrospectively reviewed the medical records of breast cancer patients with clinical T1-2N1 disease who received NAC followed by surgery and postoperative radiotherapy between 2005 and 2017. Patients with 1-3 pathologically positive lymph nodes (ypN1) after axillary dissection were included. Univariate and multivariate analyses were performed to identify the prognostic factors for locoregional recurrence-free survival (LRRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS), and overall survival (OS).

RESULTS

The median follow-up duration was 88.9 months (range, 5.0-200.1). A total of 245 patients were included and RNI was administered in 84.5% (n = 207). Lymphatic invasion and extranodal extension were more frequent in patients who received RNI compared with those who did not (p = 0.009 and p < 0.001, respectively), while other patient and tumor characteristics were similar between the two groups. On multivariate analysis, histologic grade was identified as a significant prognostic factor for LRRFS (p = 0.045) and lymphatic invasion was significantly associated with DMFS (p = 0.029). However, RNI was not associated with any of the survival outcomes. The 5-year LRRFS, DMFS, DFS, and OS in the RNI and non-RNI groups were 89.5% vs. 97.2%, 84.2% vs. 91.6%, 81.7% vs. 91.6% and 91.1% vs. 100%, respectively (all p > 0.05).

CONCLUSION

RNI was not associated with additional survival benefit in cT1-2N1 breast cancer patients with ypN1 disease after NAC. These findings warrant further validation.