The OPBC-07/microNAC Study

Inclusion Criteria: * Consecutive women and men aged 18 years or older with a diagnosis of stage I-III breast cancer (any histological and receptor subtype) * For Clinically Node negative (cN0) at presentation: any axillary staging technique including palpation is allowed. Dual tracer mapping is not required for Sentinel Lymph Node Biopsy (SLNB) * For Clinically Node positive (cN+) at presentation: Biopsy proven confirmation is required. Staging techniques include: SLNB with dual mapping or targeted axillary dissection (Targeted Axillary Dissection, TAD: imaging-guided localization of sampled node in combination with Sentinel Lymph Node procedure with or without dual mapping) or the Marking Axillary Lymph Nodes with Iodine Seeds (MARI) procedure * Completed neoadjuvant chemotherapy * Residual micrometastases detected on SLNB or TAD or MARI (on frozen section or final pathology) * Concomitant presence of Isolated Tumor Cells (ITCs) and micrometastases in other sentinel lymph nodes is allowed * Received axillary treatment with completion axillary lymph node dissection (ALND), axillary Radiotherapy (ART), both or none * At least 1-year follow-up (inclusion should end in May 2023) * Had surgery at any time point until May 2023 at the latest * Prior history of stage I-III (not stage IV) breast cancer is allowed Exclusion Criteria: * Did not undergo SLNB/TAD/MARI (e.g., went straight to ALND or ART) * Presence of ITCs alone or macrometastases on the sentinel nodes (or TAD nodes or MARI node) * Stage IV disease at presentation * Inflammatory breast cancer at presentation * Neoadjuvant endocrine therapy * Micrometastases detected by One-step nucleic acid amplification (OSNA)