Regional node recurrence after sentinel lymph node biopsy for ycN0 patients treated with primary chemotherapy in cT1-3N1M0 breast cancer (second report from SHARE study).

576 Background: Axillary management after sentinel lymph node biopsy (SLNB) is still debated for clinically node-positive breast cancer (BC) patients treated with neoadjuvant chemotherapy (NAC). The Japanese Society for Sentinel Node Navigation Surgery conducted a prospective non-randomized phase 2 study (SHARE study, UMIN000030558). False-negative rate (FNR) as the primary endpoint was reported at ASCO2023. In brief, it was 11.5% (90% confidence interval, 5.5% and 20.5%). When multimodal imaging, 1 nodal metastasis, multiple tracers, multiple sentinel lymph nodes were considered for subset analysis, the FNR was 12.1%, 9.1%, 11.1%, and 10.6%, respectively. Here we report a short-term prognosis of ycN0 BC patients. Methods: Clinical T1-3N1M0 BC was eligible. Nodal metastasis was histologically confirmed. In case of ycN0 BC, SLNB was planned and lymphatic mapping depended on each institutional practice. In cases of pN0(sn), pN0(i+)(sn) and pN1mi(sn), SLNB followed by lymph node sampling (LNS) had been allowed instead of axillary lymph node dissection (ALND). Results: Between February 2018 and May 2021, 185 patients from 19 institutes were registered. Twenty-seven cases were exculded by protocol deviation, non-ycN0 or withdrawal of SLNB. Among the 158 ycN0 cases, sentinel lymph nodes were detected in 153 cases. The median age was 52 years old. Clinical stage was IIA in 40 cases, IIB in 105 and IIIA in 8. Luminal subtype classified by ER, PR and HER2 expression was found in 60 cases, HER2 in 34, Luminal-HER2 in 35 and triple-negative in 24. SLNB alone was performed in 37 cases, SLNB and LNS in 72 and SLNB followed by ALND in 44. Regional nodal irradiation was planned in 63 cases. At the median follow-up of 24 months, 13 cases relapsed and 5 died of BC. Regional node recurrence-free survival rate at 2 years after surgery, disease-free survival rate and overall survival rate were 98.6%, 92.6% and 97.3%, respectively. Conclusions: SLNB-guided axillary management is feasible and safe in ycN0 BC after NAC. Clinical trial information: 000030558 .