The role of regional nodal irradiation in clinically node-positive breast cancer patients who undergo neoadjuvant chemotherapy and breast-conserving surgery.

[PURPOSE] The use of neoadjuvant chemotherapy (NAC) in breast cancer management has increased, leading to uncertainties in adjuvant treatment benefits.

[METHODS] We reviewed (cN +) stage II-III breast cancers that underwent NAC and breast-conserving treatment (BCT) between 2010 and 2020 in the National Cancer Database (NCDB). Overall survival (OS) was compared between those who did and did not receive regional nodal irradiation (RNI).

[RESULTS] The 7137 cN + patients had a mean age of 54.3 ± 10.9. Breast and nodal pCR rates were 25.9% and 35%. RNI was administered in 57.7% (50.0% of the ypN0 and 61.9% of the ypN +). The mean number of nodes removed was 10.3 ± 7.7 in the RNI + and 9.5 ± 7.6 in the RNI- groups (p < 0.01). The mean number of positive nodes was 2.5 ± 4.0 in the RNI + and 1.8 ± 3.5 in the RNI- groups (p < 0.01). In a median follow-up of 68 months, RNI + patients had a worse OS than RNI- patients (79.9% vs. 84.4%, p < 0.001). In the ypN0 population, there was no OS difference between RNI + and RNI- groups (p = 0.4), however, ypN + patients had worse OS if they were RNI + than RNI- (p = 0.007).

[CONCLUSION] RNI does not improve OS in cN + patients undergoing a complete response from NAC after BCT. Although recurrence cannot be assessed via this data set, these results support individualized decisions to omit RNI in ypN0 patients following NAC and BCT and emphasize the need for further investigation into the potential benefits or harms of RNI in ypN + patients treated with NAC and BCT.