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.