Abraxane® With or Without Mifepristone for Advanced, Glucocorticoid Receptor-Positive, Triple-Negative Breast Cancer

Primary Objective: To compare the progression free survival (PFS) of patients treated with nab-paclitaxel + placebo and patients treated with nab-paclitaxel + mifepristone. Secondary Objectives: 1. To correlate percentage glucocorticoid receptor (GR) positivity in the most recent metastatic tumor biopsy (or in primary tumor if only primary tumor is available) with PFS in mifepristone and placebo groups. 2. To perform an exploratory assessment of overall response rate in both groups. 3. To collect information regarding overall survival in both treatment cohorts.