Letrozole in Treating Postmenopausal Women With Stage I, II or III Breast Cancer That Can Be Removed by Surgery

OBJECTIVES: Primary To determine that in breast tumors that continue to exhibit high proliferation (i.e., Ki67) upon hormone deprivation (with letrozole), their gene expression and/or a mutational or proteomic signatures will harbor molecules or 'pathways' that are biomarkers of resistance to endocrine therapy or a cause of it. The ultimate goal of these aims is to identify clinically-targetable pathways which can be exploited to enhance responses and survival in patients with ER+ breast cancer. OUTLINE: Patients receive oral letrozole once daily for 7-21 days in the absence of disease progression or unacceptable toxicity. Within 24 hours after the last dose of letrozole, patients undergo total mastectomy or segmental resection with lymph node evaluation. Pre-treatment diagnostic breast tissue is obtained. Patients undergo treatment and then undergo standard of care mastectomy or lumpectomy. Pre and post treatment tumor tissue samples are analyzed for Ki67, P-ER, ER, progesterone receptor (PR), and caspase 3 by immunohistochemistry; and RNA microarray.