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): 18.0-65.0,  Estrogen Receptor Positive Breast Cancer Progesterone Receptor Positive Tumor Recurrent Breast Carcinoma Stage IA Breast Cancer Stage IB Breast Cancer Stage IIA Breast Cancer Stage IIB Breast Cancer Stage IIIA Breast Cancer Premenopausal women (estradiol [E2] in the premenopausal range [according to institution parameters]) who meet the following Patients who did not receive chemotherapy should be randomized within 12 weeks after definitive surgery; such patients should have estradiol (E2) in the premenopausal range following surgery; the only patients who do not require testing of estradiol (E2) to confirm premenopausal status are those who have been menstruating regularly during the 6 months prior to randomization and have not used any form of hormonal contraception or any other hormonal treatments during the 6 months prior to randomization Patients who received prior adjuvant and/or neoadjuvant chemotherapy should be randomized after completing chemotherapy and within 8 months of the final dose of chemotherapy as soon as premenopausal status is confirmed; all such patients should have premenopausal status confirmed by an estradiol (E2) in the premenopausal range between 2 weeks and 8 months after completing chemotherapy Adjuvant trastuzumab (Herceptin ®) is allowable, and is not considered to be chemotherapy for timing determination Patients with temporary chemotherapy-induced amenorrhea who regain premenopausal status within eight months of the final dose of chemotherapy are eligible; (please note that some patients taking tamoxifen or aromatase inhibitors, even without evidence of menses, may have ovarian function recovery following chemotherapy and resume estradiol secretion); in patients wishing to participate in the study, with postmenopausal hormone levels shortly after chemotherapy, it is recommended to recheck their estradiol level at a later timepoint within 8 months of completing chemotherapy, even in the absence of return of menses Histologically proven, resected breast cancer; pathology material should be available for submission for central review as part of the quality control measures for this protocol Patients must have hormone receptor positive tumors; if there is more than one breast tumor, each tumor must be hormone receptor positive; hormone receptors must be determined using immunohistochemistry; estrogen receptor (ER) and/or progesterone receptor (PgR) must be greater than or equal to 10% of the tumor cells positive by immunohistochemical evaluation; biochemical determination alone is not acceptable The tumor must be confined to the breast and axillary nodes without detected metastases elsewhere, with the exception of tumor detected in internal mammary chain nodes by sentinel node procedure; patients who received neoadjuvant therapy must have had operable disease prior to neoadjuvant treatment to be eligible; patients who had a pathological evaluation with tru cut or core biopsy of invasive breast cancer prior to neoadjuvant therapy and were found to have no invasive tumor in the pathological specimen from definitive surgery are eligible; for these patients, pre-neoadjuvant tumor characteristics will be used for defining eligibility; in case of persistent disease, pathology findings from the definitive surgery should be used Patients must have had proper surgery for primary breast cancer with no known clinical residual loco-regional disease A total mastectomy; radiotherapy is optional after mastectomy OR  Patients who are postmenopausal (i.e., do not have an estradiol [E2] level in the premenopausal range) after surgery or after chemotherapy, whichever is later Patients with distant metastatic disease Patients with locally advanced inoperable breast cancer including inflammatory breast cancer or supraclavicular node involvement or with enlarged internal mammary nodes (unless pathologically negative) are not eligible; patients with involved internal mammary nodes detected by sentinel node biopsy that are not enlarged are eligible Patients with positive final margins (referring to only DCIS and invasive cancer, not lobular breast carcinoma in situ [LCIS]), except as noted; DCIS at a margin is permitted if a complete mastectomy has been performed Patients with clinically detectable residual axillary disease Patients with a history of prior ipsilateral or contralateral invasive breast cancer; patients with synchronous bilateral invasive breast cancer (diagnosed histologically within 2 months) are eligible if the bilateral disease meets all other Patients with previous or concomitant invasive malignancy are not eligible; the exceptions are patients with the following (and only the following) malignancies (previous or concomitant) who are eligible if adequately treated Basal or squamous cell carcinoma of the skin In situ non-breast carcinoma without invasion Contra