Inclusion Criteria:

          1. A history of histological proven AR-positive (i.e. >10% staining), HER2-negative
             metastatic breast cancer (preferably assessment on fresh metastasis biopsy,
             alternatively archival metastasis biopsy)

          2. Tumor progression after at least one line of systemic treatment

          3. Measurable disease according to RECIST 1.1; or evaluable disease

          4. Age ≥ 18 years

          5. Postmenopausal status defined as one of the following:

               -  Age ≥60 years

               -  Previous bilateral oophorectomy

               -  Age <60 years and amenorrhea for >12 months in the absence of interfering
                  hormonal therapies (such as LH-RH agonists and ER-antagonists

               -  Age <60 years using ER antagonists should have amenorrhea for >12 months and FSH
                  >24U/L and LH>14U/L

          6. Adequate hematological, renal and liver function as follows:

               -  Absolute neutrophil count > 1.5 x 109/L

               -  Platelet count >100 x 109/L

               -  White blood cell count >3 x 109/L

               -  AST and ALT <3.0 x upper limit of normal (ULN)

               -  Alkaline phosphatase <2.5 x ULN

               -  Creatinine clearance >50mL/min

               -  Lipase/amylase <1/5 x ULN

               -  Protrombin time, partial tromboplastin time and INR <1.5 x ULN

          7. Written informed consent

        Exclusion Criteria:

          1. Unable to comply with the protocol

          2. Evidence of central nervous metastases

          3. Presence of life-threatening visceral metastases

          4. Corrected QT interval (QTc) >500millliseconds at screening

          5. Recent history of cardiac disease, including myocardial infarction, unstable angina
             pectoris or uncontrolled arrhythmia within 6 months prior to screening; or evidence of
             severe congestive heart failure with New York Heart Association severity
             classification > class I.

          6. Recent history of trombo-embolic events within 6 months prior to screening

          7. Hepatic impairment (Child-Pugh Class B or C)

          8. Severe concurrent disease, infection, co morbid condition that, in the judgment of the
             investigator would make the patient inappropriate for enrollment

          9. The concomitant use of strong CYP3A4 inhibitors (see table 1)

         10. Previous anti-androgen treatment

         11. Concurrent use of ER-directed anti hormonal therapies

         12. Radiotherapy or major surgery within 4 weeks before baseline PET scanning