LBA5 - The role of radiation therapy in clinically node-positive, pathological negative nodes after neoadjuvant chemotherapy in breast cancer patients: In sentinel node biopsy and trastuzumab era

Abstract

BackgroundAlthough current guidelines recommend deciding on postmastectomy radiation therapy (PMRT) or regional nodal irradiation (RNI) after breast conserving surgery (BCS) depending on initial clinical stages before neoadjuvant chemotherapy (NAC), it is controversial whether adjuvant radiation therapy (RT) can be omitted for patients with excellent response. This retrospective study evaluates if PMRT or RNI after BCS significantly reduces locoregional recurrence rate in patients with clinically positive, pathologic negative lymph nodes (LNs) after NAC. MethodsFrom 1999 to 2016, 1831 women with breast cancer underwent NAC and surgery. Of them, 427 patients with clinically node-positive and pN0 disease were analyzed. ResultsMedian follow-up was 65.4 months. The 5-year locoregional relapse (LRRFS) and disease-free survival (DFS) rates were 96.9% and 88.3%, respectively. In patients with an initial nodal stage of cN2-3, RT significantly reduced LRR, with a hazard ratio (HR) of 0.132 (p = 0.009). However, RT was not shown to be effective in the cN1 group (HR = 0.893, p = 0.9). RT did not improve DFS, regardless of cN stage. PMRT/RNI was defined as the combined set of patients who received PMRT or received RT, including regional nodal irradiation (RNI) after BCS; the effects of PMRT/RNI were analyzed. PMRT/RNI significantly reduced LRR in the cN2-3 patient group (HR = 0.175, p = 0.03), but there was no significant effect for cN1 disease. Among 173 patients who underwent mastectomy, there were 108 and 65 patients, respectively, who received RT or no RT. Among all patients, PMRT had no effect on LRR (p = 0.7). However, among cN2-3 patients, PMRT significantly lowered LRR (HR = 0.10, p = 0.02), while there was no significant effect in cN1 patients. ConclusionsIn analysis of all patients and of mastectomy patients, RT consistently improved local control rate in the cN2 and higher patient group. Similar results were obtained in the combined analysis of PMRT and RNI after BCS. Therefore, in ypN0 patients graded cN2 or higher, RT including RNI is predicted to be absolutely necessary. No conclusion could be reached for cN1 disease. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.