Nab-Paclitaxel with or without Mifepristone in Treating Patients with Glucocorticoid Receptor Positive Stage IV or Stage III Triple-Negative Breast Cancer That Cannot Be Removed by Surgery

Inclusion Criteria

• Patients must have histologically or cytologically confirmed breast cancer with stage IV or unresectable stage III disease
• Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) as >= 20 mm with conventional techniques or as >= 10 mm with spiral computed tomography (CT) scan, magnetic resonance imaging (MRI), or calipers by clinical exam; to be considered pathologically enlarged and measurable, a lymph node must be >= 15 mm in short axis when assessed by CT scan (CT scan slice thickness recommended to be no greater than 5 mm)
• Triple-negative breast cancer (defined as estrogen receptor [ER] and progesterone receptor [PR] < 10% positive; HER2 0-1+ by immunohistochemistry [IHC] or fluorescence in situ hybridization [FISH] ratio < 2.0)
• Patients may have received adjuvant chemotherapy and up to two prior chemotherapy for metastatic or locally recurrent disease; no prior nab-paclitaxel will be allowed. Prior mifepristone will be allowed
• Eastern Cooperative Oncology Group (ECOG) performance status =< 2 (Karnofsky >= 60%)
• Absolute neutrophil count >= 1,500 cells/mm^3
• Platelets >= 100,000/mcL
• Hemoglobin > 9.0 g/dL
• Total bilirubin =< 1.5 mg/dL * For patients with Gilbert’s syndrome, elevated total bilirubin is acceptable provided conjugated bilirubin is < 1.5 X ULN
• Alkaline phosphatase =< 2.5 x upper limit of normal (ULN) or =< 5 X ULN if bone metastases (mets) are present
• Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) =< 2.5 ULN or =< 5 x ULN if liver mets are present
• Creatinine =< institutional upper limit of normal OR creatinine clearance >= 60 mL/min/1.73 m^2 for patients with creatinine levels above institutional normal
• International normalized ratio (INR) =< 1.5
• Females of child-bearing potential (defined as a sexually mature woman who (1) has not undergone hysterectomy [the surgical removal of the uterus] or bilateral oophorectomy [the surgical removal of both ovaries] or (2) has not been naturally postmenopausal for at least 24 consecutive months [i.e., has had menses at any time during the preceding 24 consecutive months]) must: * Either commit to true abstinence from heterosexual contact (which must be reviewed on a monthly basis), or agree to use, and be able to comply with, effective contraception without interruption, 28 days prior to starting investigational product (IP) therapy (including dose interruptions), and while on study medication or for a longer period if required by local regulations following the last dose of IP; and * Have a negative serum pregnancy test (beta-human chorionic gonadotropin [hCG]) result at screening and agree to ongoing pregnancy testing during the course of the study, and after the end of study therapy; this applies even if the subject practices true abstinence from heterosexual contact
• Male subjects must practice true abstinence or agree to use a condom during sexual contact with a pregnant female or a female of childbearing potential while participating in the study, during dose interruptions and for 6 months following protocol discontinuation, even if he has undergone a successful vasectomy * True abstinence is acceptable when this is in line with the preferred and usual lifestyle of the subject; (periodic abstinence (eg, calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception)
• Patients must have < grade 2 pre-existing peripheral neuropathy (per Common Terminology Criteria for Adverse Events [CTCAE])
• Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria

• Patients who are receiving any other investigational agents
• Patients who have had chemotherapy or radiotherapy within 2 weeks prior to entering the study or those who have not recovered from adverse events due to agents administered more than 4 weeks earlier
• Patients with a “currently active” second malignancy other than non-melanoma skin cancers; patients are not considered to have a “currently active” malignancy if they have completed therapy and are free of disease for >= 3 years
• Patients with known brain metastases will be eligible as long as they have completed radiation to the brain, and have been off of corticosteroid therapy for at least 7 days
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to mifepristone or paclitaxel/nab-paclitaxel; patients with a history of mild infusion reactions with paclitaxel who were able to continue to receive paclitaxel with corticosteroid premedication will be eligible to participate, as these cases were likely related to Cremophor and not paclitaxel
• Mifepristone can both inhibit CYP3A4 and induce CYP3A4; addition of mifepristone to a pre-existing drug regimen may cause a mild and temporary increase in plasma drug concentration of drugs with significant CYP3A4 metabolism; medications that are strong inducers of CYP3A4 such as carbamazepine, oxcarbazepine, phenobarbital, phenytoin, primidone, rifabutin, rifampin, rifapentine, St. John's wort may decrease plasma mifepristone levels; strong CYP3A4 inhibitor medications are expected to cause the largest increases in plasma mifepristone concentrations * Mifepristone may increase the plasma drug concentration of concomitant medications with metabolism mediated by CYP2C9/CYP2C8; drugs with the largest increases will be those whose metabolism is largely or solely mediated by CYP2C9/2C8 and include: non-steroidal anti-inflammatory drugs (NSAIDs) and warfarin
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
• Pregnant women are excluded from this study
• Breastfeeding should be discontinued if the mother wishes to participate in this study
• Human immunodeficiency virus (HIV)-positive patients on combination antiretroviral therapy are ineligible; appropriate studies will be undertaken in patients receiving combination antiretroviral therapy when indicated
• No history of long-term use of corticosteroids or concurrent short term use of corticosteroids is allowed