Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Stage II Breast Cancer Stage IIIA Breast Cancer Pre-Registration Clinical stage T1-3 N1 M0 breast cancer at diagnosis (prior to the start of neoadjuvant chemotherapy) by American Joint Committee on Cancer (AJCC) staging 7th edition No inflammatory breast cancer No other malignancy within 5 years of registration with the exception of basal cell or squamous cell carcinoma of the skin treated with local resection only or carcinoma in situ of the cervix All patients must have had an axillary ultrasound with fine needle aspiration (FNA) or core needle biopsy of axillary lymph nodes documenting axillary metastasis at the time of diagnosis, prior to or at most 14 days after starting neoadjuvant chemotherapy * Note: Biopsy of intramammary nodes does not fulfill Patients must have had estrogen receptor, progesterone receptor and HER2 status (by immunohistochemistry [IHC] and/or in situ hybridization [ISH]) evaluated on diagnostic core biopsy prior to start of neoadjuvant chemotherapy * Note: If HER2 status has not been clearly determined (i.e. equivocal/indeterminate), then patients should not be enrolled Patients must have completed all planned neoadjuvant chemotherapy prior to surgery; sandwich chemotherapy is not allowed (i.e. anthracycline/cytoxan or taxane chemotherapy planned to be given after surgery); patients must have completed at least 4 cycles of neoadjuvant chemotherapy consisting of an anthracycline and/or taxane-based regimen without evidence of disease progression in the breast or the lymph nodes * Note: Delays/dose modifications due to toxicities/adverse events are allowed as long as a minimum of 4 cycles of neoadjuvant chemotherapy is administered; more than 4 cycles of neoadjuvant chemotherapy (NAC) may be administered at the discretion of the treating medical oncologist Patients with HER-2 positive tumors must have received neoadjuvant trastuzumab, or trastuzumab + pertuzumab, or other approved anti-HER-2 therapy (either with all or with a portion of the neoadjuvant chemotherapy regimen); therapy must be Food and Drug Administration (FDA)-approved targeted anti-HER2 therapy, but additional therapies are allowed as are non-trastuzumab regimens if administered in the context of an Institutional Review Board (IRB)-approved clinical trial All patients must have a clinically negative axilla (no bulky adenopathy) on physical examination documented at the completion of neoadjuvant chemotherapy * Note: an ultrasound of the axilla is not required at completion of neoadjuvant chemotherapy; if performed, its findings do NOT impact No more than 8 weeks of neoadjuvant endocrine therapy prior to the start of neoadjuvant chemotherapy