Examination of Breast Cancer Cells of Pre-menopausal and Post-menopausal Women Before and After Exposure to Tamoxifen or Fulvestrant.

Inclusion Criteria: * Written informed consent prior to beginning specific protocol procedures, including expected cooperation of the patients for the study treatment regimen and follow-up, must be obtained and documented according to the local regulatory requirements * Adult women greater than 18 years old * Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2 * New diagnosis of invasive cyclin D1 +, ER+, PR +/-, Her2- breast cancer * Cyclin D1 positive as defined as a total immunohistochemical score of 5 or greater * Hormone receptor positive as defined as ≥ 10% positive stained cells * HER2-normal (IHC score 0-1 or FISH negative \[in-situ hybridization (ISH) ratio \<= 2.0 status\]) * Tumor size at least 5 mm with planned primary surgery at Mount Sinai * A negative urine dipstick pregnancy test Exclusion Criteria: * Estrogen receptor negative invasive breast carcinoma as defined as less than 10% stained cells * Prior antiestrogen therapy * Tumor size less than 5 mm * Prior diagnosis of thrombosis or known hypercoagulable state * Known history of bleeding diathesis * Known liver disease * Prior treatment with neoadjuvant therapy * Inflammatory breast cancer defined as clinically significant erythema of the breast and/or documented dermal lymphatic invasion (not direct skin invasion by tumor or peau d'orange without erythema). * Current severe or uncontrolled systemic disease * Pregnancy or lactation period. Patients of childbearing potential must implement adequate non-hormonal contraceptive measures (barrier methods, intrauterine contraceptive devices) during study treatment. * Prior malignancy (including invasive or ductal in-situ breast cancer) within 5 years prior to randomization, except curatively treated basal cell carcinoma of the skin and carcinoma in situ of the cervix.