Preoperative Fulvestrant With or Without Enzalutamide in ER+/Her2- Breast Cancer

Inclusion Criteria:

ER+ Her2- breast cancer
Stage at least T2 or greater
Planned to get local surgery
Postmenopausal, or if pre- or peri- menopausal, then will need to have concurrent ovarian suppression.
At least 18 years of age
Not on anticoagulants
PS 0-2
Able to swallow study drug and comply with study requirements
ANC >1000/uL, platelets >75,000/uL at screening visit
Total bilirubin < 1.5 times upper limit of normal (ULN) at the screening visit unless an alternate nonmalignant etiology exists (eg, Gilbert's disease)
Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) < 3 times ULN or < 5 times ULN if patient has documented liver metastases
Creatinine < 1.5 times ULN
INR < 1.5 times ULN, or if on warfarin, can safely transition off for biopsy
Willing to donate blood for research at 4 time points
Willing to undergo core biopsies for research at study entry and at ~4 weeks.
Willing to donate tissue to research from the surgical specimen
Written informed consent obtained prior to biopsies and blood samples

Exclusion Criteria:

Current or previously treated brain or leptomeningeal metastases
History of seizures
Prior treatment with an anti-androgen (abiraterone, ARN-509, bicalutamide, enzalutamide, ODM-201, TAK-448, TAK-683, TAK-700, VT-464).
Systemic estrogens or androgens within 14 days before initiating therapy. Vaginal estrogens are allowed if necessary for patient comfort.