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,  HER2/Neu Positive Progesterone Receptor Positive Recurrent Breast Carcinoma Stage IA Breast Cancer AJCC v7 Stage IB Breast Cancer AJCC v7 Stage IIA Breast Cancer AJCC v6 and v7 Stage IIB Breast Cancer AJCC v6 and v7 Stage IIIA Breast Cancer AJCC v7 Stage IIIC Breast Cancer AJCC v7 Patients should have a life expectancy of at least 10 years, excluding their diagnosis of breast cancer; (comorbid conditions should be taken into consideration, but not the diagnosis of breast cancer) Women of reproductive potential must agree to use an effective non-hormonal method of contraception (for example condoms, some intrauterine devices, diaphragms, tubal ligation, vasectomized partner, or abstinence) during therapy and for at least 6 months (Arm 1 patients) and for at least 7 months (Arm 2 patients) after the last dose of study therapy (chemotherapy or trastuzumab) Submission of tumor samples from the breast surgery is required for all patients; therefore, the local pathology department policy regarding release of tumor samples must be considered in the screening process; patients whose tumor samples are located in a pathology department that by policy will not submit any samples for research purposes should not be approached for participation in the B-47 trial The patient must have signed and dated an Institutional Review Board (IRB)-approved consent form that conforms to federal and institutional guidelines Eastern Cooperation Oncology Group (ECOG) performance status of 0 or 1 The tumor must be unilateral invasive adenocarcinoma of the breast on histologic examination All of the following staging (according to the 7th edition of the American Joint Committee on Cancer [AJCC] Cancer Staging Manual) must be met By pathologic evaluation, primary tumor must be pT1-3 By pathologic evaluation, ipsilateral nodes must be pN0, pN1 (pN1mi, pN1a, pN1b, pN1c), pN2a, pN2b, pN3a, or pN3b If pN0, one of the following must be met  Primary tumor with any of the following HER2 testing results IHC staining intensity on all evaluations of specimens on evaluation of any specimen ISH with a ratio of HER2 to CEP17 >= 2.0 on evaluation of any specimen ISH result indicating HER2 gene copy number >= 4 per nucleus on evaluation of any specimen T4 tumors including inflammatory breast cancer Definitive clinical or radiologic evidence of metastatic disease NOTE: Chest imaging (mandatory for all patients) and other imaging (if required) must have been performed within 90 days prior to randomization Synchronous or previous contralateral invasive breast cancer (patients with synchronous and/or previous contralateral DCIS or LCIS are eligible)