Inclusion Criteria:

          -  Histologically or cytologically confirmed estrogen/progesterone receptors (ER/PR) +/-;
             human epidermal growth factor receptor 2 (HER2)-, metastatic breast cancer.

          -  Metastatic disease that is evaluable on imaging. May have measureable 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 CT scan, MRI,
             or calipers by clinical exam. Patients can also have non-measurable disease including
             bone only metastatic disease, evaluated by bone scan, PET or MRI.

          -  Any number of prior endocrine therapies in the metastatic setting are allowed. The
             patient must not have received any prior chemotherapy agents in the metastatic
             setting. Prior treatment with adjuvant docetaxel or paclitaxel is allowed if disease
             relapse occurred greater than 12 months from the completion of adjuvant therapy.

          -  Age ≥18 years.

          -  Eastern Cooperative Oncology Group (ECOG) performance status ≤1 (Karnofsky ≥60%).

          -  Life expectancy of greater than 4 months.

          -  Patients must have normal organ and marrow function as defined below: leukocytes
             ≥3,000/mcL, absolute neutrophil count ≥1,500/mcL, platelets ≥100,000/mcL, total
             bilirubin within normal institutional limits, aspartate aminotransferase AST(SGOT)/
             alanine aminotransferase ALT(SGPT) ≤2.5 X institutional upper limit of normal,
             creatinine within normal institutional limits OR creatinine clearance ≥60 mL/min/1.73
             m^2 for patients with creatinine levels above institutional normal.

          -  Patients with known brain metastases will only be eligible after their tumors have
             been treated with definitive resection and/or radiotherapy and they are neurologically
             stable for at least 1 month off steroids.

          -  Male and female subjects of child producing potential must agree to use adequate forms
             of contraception or avoidance of pregnancy measures prior to study entry, while
             enrolled on study and for a minimum of one month after completion of the study.

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

        Exclusion Criteria:

          -  Patients who have had chemotherapy for the treatment of metastatic breast cancer are
             not eligible. Patients who have had radiotherapy within 3 weeks prior to entering the
             study or those who have not recovered from adverse events due to agents administered
             more than 3 weeks earlier are not eligible.

          -  Patients who are currently receiving any other investigational agents.

          -  Patients with known active, untreated brain metastases should be excluded from this
             clinical trial. Those with previously treated inactive brain metastases with no
             evidence of active disease documented on brain MRI at least 4 weeks after radiation
             and off all steroids may be eligible.

          -  History of allergic reactions attributed to compounds of similar chemical or biologic
             composition to docetaxel or tryptophan containing substances. This would include
             L-tryptophan or 5-hydroxy-tryptophan supplements. Also patients with a history of
             severe hypersensitivity reactions to docetaxel or to other drugs formulated with
             polysorbate 80 are excluded.

          -  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 because indoximod is an immunoregulatory
             agent with the potential for abortifacient effects due to fetal rejection by the
             maternal immune system. Because there is an unknown but potential risk for adverse
             events in nursing infants secondary to treatment of the mother with indoximod,
             breastfeeding should be discontinued if the mother is treated with indoximod. Also,
             docetaxel and paclitaxel are category D cytotoxic agents and are not administered to
             pregnant females.

          -  Known HIV-positive patients and those with other acquired/inherited immunodeficiencies
             are ineligible due to the possibility of affecting the response to indoximod and the
             higher risk of active opportunistic infections.

          -  Patients with more than one active malignancy at the time of enrollment.

          -  Patients who have received any prior experimental active immunotherapy consisting of
             targeted monoclonal antibodies (ipilimumab) or pharmaceutical compounds are excluded.

          -  Patients with any active autoimmune disease (i.e. psoriasis, extensive atopic
             dermatitis, asthma, inflammatory bowel disease (IBD), multiple sclerosis (M.S.),
             uveitis, vasculitis), chronic inflammatory condition, or any condition requiring
             concurrent use of any systemic immunosuppressants or steroids for any reason would be
             excluded from the study. Any patient with an allo-transplant of any kind would be
             excluded as well. This would include those with a xenograft heart valve to avoid the
             potential risk of any immune reaction causing valvular degeneration. Mild-intermittent
             asthma requiring only occasional beta-agonist inhaler use or mild localized eczema
             will not be excluded.