Abstract PS6-06: Upstage of N-Stage by Diagnostic Axillary Lymph Node Dissection in Patients w/ Isolated Tumor Cells or Micrometastases in Sentinel/Target Lymph Node after Neoadjuvant Chemotherapy - Results from the Prospective Multicenter AXSANA / E

Abstract Introduction: The role of completion axillary lymph node dissection (cALND) in patients with low volume residual disease in the sentinel (SLN) or target lymph node (TLN) after neoadjuvant chemotherapy (NACT) is a matter of controversial debate. While increasing evidence suggests no therapeutic benefit from cALND, additional lymph node surgery is also performed for diagnostic purposes to identify patients for post-neoadjuvant systemic treatment or regional radiotherapy. Material and Methods: We analyzed the conversion rate of patients with isolated tumor cells (ITCs) or micrometastases in the SLN or TLN to a higher nodal (N)-stage by cALND from the prospective multicenter AXSANA trial (NCT04373655), which compares different axillary surgical staging procedures (ALND, SLN biopsy (SLNB) and targeted axillary dissection (TAD)) after NACT in patients with initially positive axillary lymph nodes. Results: 5,328 patients from 291 study sites in 26 countries were included in the AXSANA study between June 2020 and March 3rd, 2024. Of these, 2,193 had completed surgery including SLNB or TAD at the time of analysis. All datasets were monitored. 51 out of 2,193 patients (2.3%) were ypN0(i+)(sln/tln) stage and 153 out of 2,193 (7.0%) were ypN1(mi)(sln/tln). cALND was performed in 16/51 patients (31.4 %) with isolated tumor cells (ITC) and 71/153 (46.4 %) women with micrometastases in the SLN or TLN. Among 16 patients with a ypN0(i+)(sn/tln) stage who underwent cALND, 3 (18.8 %) had further non-SLN/TLN involvement including 2 with additional ITCs and 1 with macrometastatic lymph node involvement. 8 out of 16 patients (50%) achieved complete response in the breast (breast-pCR). The only macrometastasis was found in a patient with a non-pCR in the breast. Overall, 1 out of 16 patients with ypN0(i+)(sln/tln) stage was upgraded to ypN1 (6.25 %) by cALND. Among patients with a breast-pCR, no patients’ N-stage increased to a higher stage. Among 71 patients with a ypN1(mi)(sln/tln) stage who underwent cALND, 28 women (39.4 %) had further non-SLN/TLN involvement, 1 (1.4 %) had additional ITCs, 17 micrometastatic (23.9 %) and 10 (14.1 %) macrometastatic non-SLN/TLN disease. 18 out of 71 patients in this subgroup (25.4 %) achieved breast-pCR. Of these, 7 patients had additional micro- and 1 patient macrometastatic non-SLN/TLN involvement (38.9 % and 5.6 % respectively). One patient converted to a ypN1-stage (5.6 %) and no patient to a ypN2/3-stage. Among 53 patients without breast-pCR, 10 women had further micrometastatic and 9 patients additional macrometastatic involvement (18.9 % and 17.0 %). Overall, 9 out of 53 patients (17 %) with a ypN1(mi)(sln/tln)-status and non-pCR in the breast were upgraded to a higher ypN-stage (3 to ypN1, 5 to ypN2, and 1 to ypN3) (22.6 %, 15.1 %, and 1.9 %, respectively). Conclusion: An upgrade of nodal stage in ypN0(i+)(sln/tln) patients is a rare event. cALND for diagnostic purposes is not justified in this group and should be discouraged, especially in patients with a breast-pCR. Also for patients with a ypN1(mi)(sln/tln)-stage, an upgrade to a higher N-stage is also rare if breast-pCR is achieved. In patients with non-pCR in the breast, cALND is associated with a higher risk for an upgrade of the nodal stage, so that diagnostic cALND may be indicated in selected patients with potential therapeutic implications. Provided that further research confirms no therapeutic benefit from cALND, additional axillary surgery for diagnostic purposes can be omitted in most patients with initially positive lymph nodes and a low tumor burden in the SLN or TLN after NACT. Citation Format: Thorsten Kuehn, Maggie Banys-Paluchowski, Nina Ditsch, Elmar Stickeler, Oreste David Gentilini, Jana de Boniface, Michael Hauptman , ldeniz Karadeniz , Markus Hahn, Marc Thill, Rosa Di Micco, Toralf Reimer, Sarah Frohlich, Esther Schmidt, Kristina Wihlfahrt, Tomasz Berger, Timo Basali, Franzsika Ruf, Angelika Rief, Michael Patrick Lux, Hans-Christian Kolberg, Isabel Rubio Rodriguez, Maria Luisa Gasparri, Michaelis Kontos, Eduard-Alexandru Bonci, Laura Niinikoski, Dawid Muraw , David Pinto, Florentina Peintinger , Ellen Schlichting , Nina Heldion, Hagigat Valiyeva Qanimat, Marian Vanhoeji, Pamela Rebaza, Bilge Aktas Sezen, Katharina Jursik, Geeta Kadayaprath, Lukas Dostalek, Ashutosh Kothari, Andraz Perhavec, Tsvetomir Ivanov, Douglas Zippel, Sarun Thongvitokomarn , Meryem Gunay Gurleyik, Annette Lebeau, Steffi Hartmann. Upstage of N-Stage by Diagnostic Axillary Lymph Node Dissection in Patients w/ Isolated Tumor Cells or Micrometastases in Sentinel/Target Lymph Node after Neoadjuvant Chemotherapy - Results from the Prospective Multicenter AXSANA / EUBREAST 3 Study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr PS6-06.