Inclusion Criteria:

- Patient must have histologically or cytologically confirmed adenocarcinoma of the
breast triple-negative (estrogen receptor [ER]-, progesterone receptor [PR]-, human
epidermal growth factor receptor 2 [HER2]-) or hormone positive/ HER2-, with evidence
of locally advanced and inoperable or metastatic disease (American Joint Committee on
Cancer [AJCC] Stage IV)

- NOTE: Triple-negative patients will be defined per American Society of Clinical
Oncology-College of American Pathologists (ASCO-CAP) Guidelines; these
guidelines state that ER and PR assays be considered positive if there are at
least 1% positive tumor nuclei in the sample on testing in the presence of
expected reactivity of internal (normal epithelial elements) and external
controls

- A patient who has a change in receptor status (e.g., PR negative to positive)
may be stratified as triple negative or hormone positive, contrary to the most
recent receptor testing, for the purposes of the study based upon the clinical
course at the discretion of the Study Chair; for HER2 assessment, a negative
result is an immuno-histochemistry staining of 0 or 1+, a fluorescence in situ
hybridization (FISH) result of less than 4.0 HER2 gene copies per nucleus, or a
FISH ratio of less than 1.8

- Patients with triple negative disease must have progressed through at least 1 prior
chemotherapy regimen (administered in the adjuvant or metastatic setting); hormone
receptor-positive patients must have progressed through two lines of hormonal therapy
(administered in the adjuvant or metastatic setting), unless otherwise eligible as
per below, and at least 1 prior chemotherapy regimen (administered in the adjuvant or
metastatic setting) with no known curative options available

- NOTE: Patients with hormone receptor-positive disease may be considered eligible
if deemed clinically hormone-resistant taking into consideration the rate of
progression of disease or a short interval of time on first line hormonal
therapy before progression, or if intolerant of hormonal therapy such that
further hormonal therapy will not be considered as part of the treatment
strategy

- In patients with metastatic disease in the liver, liver disease burden is limited to
no more than 30% of total liver volume as assessed by local review

- Patients must have measurable disease

- Life expectancy of >= 12 weeks

- Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1

- Hemoglobin (HgB) >= 9.0 g/dL

- Absolute neutrophil count (ANC) >= 1,500/mcL

- Platelet Count >= 100,000/mcL

- Total bilirubin =< 1.5 x institutional upper limit of normal (ULN)

- Serum glutamic oxaloacetic transaminase (SGOT) (aspartate aminotransferase [AST]) =<
3 x ULN

- Creatinine =< institutional ULN or creatinine clearance >= 60 mL/min using the
Modified Cockcroft-Gault formula

- Negative (serum or urine) pregnancy test done =< 7 days prior to registration, for
women of childbearing potential only

- Patient must have an accessible tumor lesion from which a biopsy specimen can be
obtained; NOTE: if baseline biopsy is attempted and is unsuccessful (eg, patient
intolerance, inadequate tissue), the patient will still be considered eligible for
the study

- Ability to understand and the willingness to sign a written informed consent document

- Willingness to provide tissue and blood samples for mandatory translational research

- Willingness to return to the enrolling institution for follow-up

Exclusion Criteria:

- Any of the following because this study involves an investigational agent whose
genotoxic, mutagenic and teratogenic effects on the developing fetus and newborn are
unknown:

- Pregnant women

- Nursing women

- Men or women of childbearing potential who are unwilling to employ adequate
contraception

- NOTE: the effects of 5-AZA and entinostat on the developing human fetus at the
recommended therapeutic dose are unknown; for this reason, should a woman become
pregnant or suspect she is pregnant while participating in this study, she
should inform her treating physician immediately

- Any of the following:

- Chemotherapy =< 3 weeks prior to registration

- Hormone therapy =< 3 weeks prior to registration

- Radiotherapy =< 3 weeks prior to registration

- Surgery =< 3 weeks prior to registration

- Nitrosoureas/mitomycin C =< 6 weeks prior to registration

- Trastuzumab =< 6 weeks prior to registration

- Bevacizumab =< 6 weeks prior to registration

- Those who have not recovered from acute adverse events to grade < 2 or baseline
due to agents administered, with exception of alopecia, unless approved by the
Protocol Chair

- NOTE: concurrent bisphosphonate therapy is allowed; concurrent ovarian
suppression therapy (i.e., Lupron or Zoladex) is also allowed at the discretion
of the Protocol Chair/designee

- Any other ongoing investigational agents

- Known sensitivity to 5-AZA, entinostat or mannitol

- Uncontrolled intercurrent illness that in the judgment of the investigator, would
make the patient inappropriate for entry into this study or interfere significantly
with the proper assessment of safety and toxicity of the prescribed regimens
including, but not limited to:

- Ongoing or active infection

- Symptomatic congestive heart failure (NYHA class II or above)

- Unstable angina pectoris

- Cardiac arrhythmia

- Psychiatric illness/social situations that would limit compliance with study
requirements

- Other co-morbid systemic illness or other severe concurrent disease

- Active malignancy other than breast cancer =< 3 years prior to registration;
EXCEPTIONS: non-melanotic skin cancer or carcinoma-in-situ of the cervix; NOTE: if
there is a history of prior malignancy, they must not be receiving other specific
treatment for their cancer

- Immunocompromised patients (other than that related to the use of corticosteroids)
including patients known to be human immunodeficiency virus (HIV) positive

- Received prior treatment with HDAC (histone deacetylase) inhibitors or demethylating
agents =< 2 weeks prior to registration

- Unstable brain metastases; NOTE: patients with brain metastases must have stable
neurologic status and magnetic resonance imaging (MRI) imaging following local
therapy (surgery or radiation) for at least 4 weeks, with no dexamethasone
requirement (stable low dose dexamethasone allowed at discretion of Study Chair);
patients with leptomeningeal disease are not eligible

- Patient taking valproic acid

- Patient who cannot swallow tablets