196P Surgical axillary intervention after neoadjuvant systemic therapy (NST) for early-stage breast cancer: Clinical significance of micrometastases - Data from five neoadjuvant studies

Axillary surgery in early breast cancer (BC) has become less radical. However, for patients (pts) undergoing NST, the optimal surgical treatment algorithm in the axilla remains uncertain and is influenced by response to NST. The significance of nodal micrometastases (ypN1mi) after NST remains controversial and detection of additional macrometastases could have impact on postneoadjuvant treatment decisions. The aim of our study was to retrospectively analyse ypN1mi occurrence in five neoadjuvant AGO B / GBG trials conducted between 2012 and 2019. Data from 3199 pts with early BC, who were enrolled in five NACT studies (GeparSepto, GeparOcto, GeparNuevo, GeparX, GeparOla), were retrospectively analyzed. Our study investigated axillary surgeries, the incidence of ypN1mi and their correlation with outcome. 3163/3199 (98.9%) patients underwent breast surgery and information available on axillary intervention and were included in our analysis. TNBC, HER2+ and HR+/HER2- BC were reported in 38.9%, 29.1% and 32.0% respectively. Nodal status upon clinical/imaging evaluation was cN0 in 66.5%, cN1 in 29.5% and cN2/cN3 in 3.9%. Sentinel lymph node biopsy (SLNB) prior to NST was performed in 44.1% (1395/3163) and after NST in 19.4%. 1746 pts did not have any axillary surgery prior to NST. After NST 612 pts had a SLNB only, 5 pts received a targeted lymph node biopsy (TLNB) only, 27 pts had a targeted axillary dissection (TAD) and 1288 pts received an axilla lymph node dissection (ALND) only. 125 pts had an ALND following SLNB, TLNB or TAD. Of the 2038 evaluable pts who had any LN surgery after NST 879 (43.1%) achieved a pathological complete response in the breast (ypT0) of which 47 (5.3%) had concurrent residual disease in the LNs (ypT0, ypN+). 2.7% had ypN1mi and 0.64% had ypN1mi as sole residual disease. During our retrospective study period, surgical standards changed to preferring SLNB in cN0 and allowing TAD in cN+ patients both after NST starting 2017 and 2019 respectively. Surgical approaches according to cN stage, axillary conversion rates according to subtypes and 5 year TTE data will be presented.