Background: Consensus on the axillary management in cN+ breast cancer patients whoconvert to ycN0 after primary systemic treatment (PST) is still lacking. A surveywas conducted to investigate the clinical practice in this setting. Materials and Methods: A web-based survey was developed by a multidisciplinary group on behalfof the European Breast Cancer Research Association of Surgical Trialists (EUBREAST),and distributed to breast surgeons and radiation oncologists via breast cancersocieties. Results: We received 345 replies from 43 countries. A majority of responderssuggest FNA/CNB before treatment (81%) while 19 % perform histologic assessmentonly in selected cases. The preferred surgical approach to the axilla in cN1patients who convert to ycN0 is targeted axillary dissection (TAD) 55%,sentinel lymph node biopsy (SLNB) 21%, axillary lymphadenectomy (ALND) (level1-2) 19%, others 5%. When SLNB is preformed, single and dual tracers are usedin 62% and 38% respectively. No minimumnumber of SLNs is required by 36 % of the surgeons, while 8% and 56% suggest toremove at least 2 or 3 SLNs respectively.For targeted lymph node biopsy (TLNB) or TAD, there is a wide heterogeneitywith regards to localization techniques. In case of multiple suspicious nodes, 65%of the responders declared to mark only one node. 47 % of responders routinelyperform an additional preoperative localization of the TLN. Imaging modalitiesto assess the ycN status are: ultrasound (67%), MRI (21%), other(12%). In caseof ambiguous finding before PST (cN+) ALND was suggested by 23 % only after routine histologicconfirmation of lymph node involvement and by 45 % without. 29% of theresponders perform SLNB/TAD/TLNB without additional axillary surgery 3%suggested different approaches. 66 % of the participants recommended ALND in ycN+ patients only after furtherhistologic confirmation, while 23 % do not perform CNB/FNA. 11 % voted forTAD/SLNB/TLNB in this setting. The decision for post-operative regionalirradiation is influenced by initial nodal lymph node status (61 %) and by acombination of pre- and post- PST assessment (39%). 21% of the responders neverirradiate level I in patients with a ypN>1 status after ALND while 37 % suggestselective use of RT and 42 % favoured RT in all patients. Target volumes forelective nodal irradiation are determined mainly based on ESTRO (61%) and RTOG(32%) guidelines.In case of macrometastatic nodal disease (ycN0ypN+) regional nodeirradiation was suggested by 59 % of the participants regardless of the numberof involved nodes. 37 % suggested RT in patients with more than 3 positive nodes,while 4% would never irradiate. After a positive TAD or SLNB radiationoncologists suggest ALND in 63 % and RT in 37%. Similar results were attainedfor ypN1mi and ypN0(i+). 34 % of the breastsurgeons suggested ALND for patientswith ypN1(mi) status after TAD/SLNB, 31 % favored RT, 23% a combination and 12%suggested omission of further reginal treatment. Remodeling fibrotic scarsrarely affect regional treatment planning. Conclusions: The results of this EUBREAST survey highlightthe wide heterogeneity in the approach to the axilla after PST, corroborate theneed for further clinical research and provide the rationale for the AXSANA(EUBREAST 3) study . Supporting Societies:. American Society of Breast Surgeons (ASBrS). Arbeitsgemeinschaft für gynäkologische Onkologie (AGO). Associazione Nazionale Italiana Senologi Chirurghi (ANISC). Collegio Italiano dei Senologi. Deutsche Gesellschaft für Radioonkologie (DEGRO). Deutsche Gesellschaft für Senologie (DGS). Global Breast Hub. Israel Breast Surgeons Society. Israel Radiation Therapy society. Swiss Society of Senology (SSS). Scuola Italiana di Senologia. Società Polispecialistica Italiana Giovani Chirurghi (SPIGC). Swedish Breast Cancer Group. The Oncoplastic Breast Consortium (OPBC)

Citation Format: Maria Luisa Gasparri, Jana De Boniface, Oreste Davide Gentilini, Orit Kaidar-Person, Philip Poortmans, Thorsten Kuehn. Perspectives on axillary management after primary systemic treatment: An international EUBREAST survey [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-01-16.