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 IB Breast Cancer Stage II Breast Cancer The patient must have signed and dated an Institutional Review Board (IRB)-approved consent form that conforms to federal and institutional guidelines The patient must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 Patient must have clinically T1-3, N1 breast cancer at the time of diagnosis (before neoadjuvant therapy); clinical axillary nodal involvement can be assessed by palpation, ultrasound, CT scan, magnetic resonance imaging (MRI), positron emission tomography (PET) scan, or PET/CT scan Patient must have had pathologic confirmation of axillary nodal involvement at presentation (before neoadjuvant therapy) based on either a positive fine needle aspirate (FNA) (demonstrating malignant cells) or positive core needle biopsy (demonstrating invasive adenocarcinoma); the FNA or core needle biopsy can be performed either by palpation or by image guidance; documentation of axillary nodal positivity by sentinel node biopsy (before neoadjuvant therapy) is not permitted Patients must have had estrogen receptor (ER) analysis performed on the primary breast tumor before neoadjuvant therapy according to current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guideline recommendations for hormone receptor testing; if negative for ER, assessment of progesterone receptor (PgR) must also be performed according to current ASCO/CAP guideline recommendations for hormone receptor testing (http://www.asco.org) Patients must have had HER2 testing performed on the primary breast tumor before neoadjuvant chemotherapy according to the current ASCO/CAP guideline recommendations for human epidermal growth factor receptor 2 testing in Breast Cancer (http://www.asco.org); patients who have a primary tumor that is either HER2-positive or HER2-negative are eligible Patient must have completed a minimum of 8 weeks of standard neoadjuvant chemotherapy consisting of an anthracycline and/or taxane-based regimen For patients who receive adjuvant chemotherapy after surgery, a maximum of 12 weeks of intended chemotherapy may be administered but must be completed before randomization; (if treatment delays occur, chemotherapy must be completed within 14 weeks); the dose and schedule of the adjuvant chemotherapy are at the investigator's discretion; Note: It is preferred that all intended chemotherapy be administered in the neoadjuvant setting Patients with HER2-positive tumors must have received neoadjuvant anti-HER2 therapy (either with all or with a portion of the neoadjuvant chemotherapy regimen), unless medically contraindicated At the time of definitive surgery, all removed axillary nodes must be histologically free from cancer; acceptable procedures for assessment of axillary nodal status at the time of surgery  Definitive clinical or radiologic evidence of metastatic disease T4 tumors including inflammatory breast cancer Documentation of axillary nodal positivity before neoadjuvant therapy by sentinel node biopsy alone N2 or N3 disease detected clinically or by imaging Patients with histologically positive axillary nodes post neoadjuvant therapy Patients with microscopic positive margins after definitive surgery Synchronous or previous contralateral invasive breast cancer or DCIS; (patients with synchronous and/or previous contralateral LCIS are eligible) Any prior history, not including the index cancer, of ipsilateral invasive breast cancer or ipsilateral DCIS treated with radiation therapy; (patients with synchronous or previous ipsilateral LCIS are eligible) History of non-breast malignancies (except for in situ cancers treated only by local excision and basal cell and squamous cell carcinomas of the skin) within 5 years prior to randomization Any radiation therapy for the currently diagnosed breast cancer prior to randomization