SENOMAC-ULTRA enrols patients who are planned for upfront surgery for a breast cancer that has spread to lymph nodes in the armpit, and that have been detected already prior to surgery by imaging, e.g. ultrasonography. In this situation, a full axillary lymph node dissection, removing more than 10 lymph nodes from the arm pit, is unnecessarily extensive in about half of the patients. More extensive surgery leads to a risk for arm lymphedema and functional problems with the arm and shoulder region, which should be avoided if not beneficial for diagnosis or prognosis. This trial seeks to ascertain that less extensive surgery, performed by only removing the first lymph node/s in the armpit (the sentinel lymph node/s) and the known metastatic lymph nodes (targeted axillary dissection, TAD), offers non-inferior survival outcomes to a full axillary lymph node dissection.

Inclusion Criteria:

• Patients with primary invasive breast cancer clinical stage II-III
• Palpable or non-palpable axillary metastases visible by ultrasound (other imaging accepted if confirmatory ultrasound is performed) and confirmed by fine needle aspiration or core biopsy
• Written informed consent
• Age ≥ 18 years

Exclusion Criteria:

• Distant metastases
• Ipsilateral metastases in internal mammary, infra- or supraclavicular lymph nodes without confirmed axillary nodal involvement
• Preoperative suspicion of extensive nodal involvement, i.e. locally advanced disease
• Nodes fixed to each other or to neighbouring structures on palpation or imaging
• History of contralateral invasive breast cancer within 5 years
• Bilateral invasive breast cancer if (i) one side meets any exclusion criteria or (ii) both sides meet all inclusion criteria
• Pregnancy
• Neoadjuvant systemic treatment (short course of neoadjuvant endocrine therapy \

IPD may be shared upon reasonable request and with all relevnt legal and ethical requirements fulfilled. No request will be accepted before the publication of the primary endpoint.