Inclusion Criteria:

          1. Signed and dated ICF

          2. Age ≥ 18 years of age, either gender

          3. Females must be postmenopausal as defined by at least one of the following:

               1. Age ≥ 60 years;

               2. Age < 60 years and cessation of regular menses for at least 12 consecutive months
                  with no alternative pathological or physiological cause; and serum estradiol and
                  follicle stimulating hormone levels within the local laboratory's normal
                  reference range for postmenopausal females;

               3. Documented bilateral oophorectomy

          4. Histologically or cytologically confirmed diagnosis of adenocarcinoma of the breast

          5. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1

          6. Adequate organ function defined as follows:

               1. Hematologic: Platelets ≥ 100 × 109/L; Hemoglobin ≥ 9.0 g/dL; Absolute neutrophil
                  count ≥ 1.5 × 109/L (without platelet transfusion or any hematopoietic growth
                  factors within previous 7 days of the hematologic laboratory values obtained at
                  the Screening Visit)

               2. Hepatic: Aspartate aminotransferase (AST) / Alanine aminotransferase (ALT)

                  ≤ 2.5 × upper limit of normal (ULN); Total or conjugated bilirubin ≤ 1.5 × ULN

               3. Renal: Serum creatinine ≤ 1.5 × ULN or creatinine clearance (CrCl) ≥ 60 mL/min

        Exclusion Criteria:

          1. Major surgery, defined as any surgical procedure that involves general anesthesia and
             a significant incision (i.e., larger than what is required for placement of central
             venous access, percutaneous feeding tube, or biopsy) within 28 days of the first
             administration of study drug

          2. Treatment with another investigational drug or other intervention within 28 days
             before the first administration of study drug

          3. Impairment of gastrointestinal (GI) function or GI disease that may significantly
             alter the absorption of oral medication, including any unresolved nausea, vomiting, or
             diarrhea that is CTCAE v.5.0 Grade > 1

          4. Myocardial infarction, symptomatic congestive heart failure (New York Heart
             Association Classification > Class II), unstable angina, or serious uncontrolled
             cardiac arrhythmia within the last 6 months of study Day 1

          5. Uncontrolled inter-current illness

          6. History or evidence of clinically significant disorder, condition, or disease that, in
             the opinion of the Investigator would pose a risk to subject safety or interfere with
             the study evaluations, procedures, or completion