Efficacy and Safety Study of Enzalutamide in Combination With Paclitaxel Chemotherapy or as Monotherapy Versus Placebo With Paclitaxel in Patients With Advanced, Diagnostic-Positive, Triple-Negative Breast Cancer

Inclusion Criteria:

* Adult women and men at least 18 years of age and willing and able to provide informed consent.
* Has advanced TNBC:
* TNBC is defined as staining by immunohistochemistry (IHC) \< 1% or Allred score \< 2 for estrogen receptor (ER) and progesterone receptor (PgR), and 0 or 1+ by IHC for human epidermal growth factor receptor 2 (HER2) or negative for gene amplification (average HER2 copy number \< 4 signals/cell; HER2:CEP17 ratio \< 2.0).
* Advanced disease is defined as locally advanced or metastatic disease not amenable to curative intent surgery or radiotherapy.
* Has diagnostic-positive status as determined by a central diagnostic testing laboratory.
* Received 0 or 1 prior line of systemic therapy in the advanced disease setting.
* Patients who received 1 prior line of therapy for locally advanced or metastatic TNBC must have objective disease progression as assessed by the investigator.
* Has measurable and/or disease that is not measurable but is evaluable using RECIST 1.1 (eg, bone metastases, pathologic lymph nodes, or skin lesions).
* Patients with nonmeasurable and nonevaluable TNBC (eg, malignant effusions or bone marrow as the only manifestations of disease) are not eligible for enrollment.
* Patients with metastatic disease limited to the bone must have disease adequately visualized by computed tomography (CT) with bone windows, magnetic resonance imaging (MRI), or x-ray.
* Has an Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1 at screening and a life expectancy of at least 3 months from randomization.

Exclusion Criteria:

* Received a taxane regimen ≥ 28 days in duration in the advanced disease setting.
* Prior taxane therapy for neoadjuvant and/or adjuvant disease is permitted.
* A single dose of a taxane given as part of an every-3-weeks regimen is permitted.
* Two doses of a taxane given as part of a once-weekly regimen is permitted.
* Had a disease-free interval of ≤ 12 months from the last dose of taxane when used as part of adjuvant therapy for patients who did not receive prior therapy for locally advanced or metastatic breast cancer.
* Has history of or known central nervous system (CNS) metastasis or active leptomeningeal disease; brain imaging is required for all patients during screening.
* Received any anticancer agent (commercially available or investigational) within 14 days before randomization.
* Received treatment with any of the following medications within 14 days before randomization:
* Estrogens, including hormone replacement therapy
* Androgens (eg, testosterone, dehydroepiandrosterone)
* Systemic radionuclides (eg, samarium, strontium)
* Had major surgery within 4 weeks before randomization.
* Has a history of another invasive cancer within 3 years before randomization, with the exception of fully treated cancers with a remote probability of recurrence.
* Has a history of a seizure condition or any condition that may predispose to seizure (eg, prior cortical stroke or significant brain trauma).
* Has known hypersensitivity to any of the enzalutamide/placebo capsule components.
* Had a hypersensitivity reaction to Cremophor EL (polyoxyethylated castor oil) or a drug formulated in Cremophor EL, such as paclitaxel, unless successfully treated and rechallenged with appropriate premedications.