The purpose of this study is to find out how often the researchers can avoid an ALND in patients with early-stage, node-positive HR+/HER2- breast cancer who are having upfront surgery. The study researchers think that, if AUS before surgery can help identify people who may have up to 3 affected lymph nodes, it will be possible to perform the less radical standard SLNB during surgery.

Inclusion Criteria:

• Patients aged ≥18 years with biopsy-proven invasive breast cancer

• Patients with cTx, cT1, or cT2 tumors with palpable ipsilateral mobile adenopathy of level I/II axillary nodes with biopsy-proven (either by pre-operative biopsy or intraoperative frozen section) nodal metastasis (cN1) who are undergoing upfront surgery

• Patients with tumors of the HR+/HER2- subtype, defined as:

  1. HR+: Positive for estrogen receptor and/or progesterone receptor staining, indicated by ≥1% immunoreactive tumor nuclei
  2. HER2-: Immunohistochemistry assay demonstrating no or faint staining in ≤10% of tumor cells (IHC 0 or 1+) or negative by dual probe in situ hybridization assay

Exclusion Criteria:

• Patients with prior ipsilateral breast cancer
• Patients who are pregnant
• Patients with stage IV disease at presentation
• Patients with advanced regional disease (cN2/cN3)

Potential research subjects will be identified by a member of the patient's treatment team, the Principal Investigator (PI), or the research team at MSKCC/participating institutions.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.