Inclusion Criteria: Provision of signed and dated, written informed consent prior to any
        mandatory study specific procedures, sampling and analyses. Aged at least 18 years. Any
        menopausal status. Pre- or peri-menopausal women must have commenced treatment with an LHRH
        agonist at least 4 weeks prior to starting study treatment and must be willing to continue
        to receive LHRH agonist therapy for the duration of the trial. Histological or cytological
        confirmation of adenocarcinoma of the breast. ER-positive according to local laboratory;
        HER-2 negative. Metastatic disease or locoregionally recurrent disease which is not
        amenable to treatment with curative intent. Disease progression after at least 6 months of
        endocrine therapy for ER+ breast cancer. Radiological or objective evidence of progression
        on or after the last systemic therapy prior to starting study treatment. Receipt of ≤2
        lines of prior chemotherapy for advanced disease. Females of child-bearing potential must
        agree to use adequate contraceptive measures, must not be breast feeding and must have a
        negative pregnancy test prior to start of dosing. Eastern Cooperative Oncology Group (ECOG)
        performance status 0-1 with no deterioration over the previous 2 weeks and minimum life
        expectancy of 12 weeks.

        Exclusion Criteria: Any cytotoxic chemotherapy, investigational agents or other anti-cancer
        drugs for the treatment of advanced breast cancer from a previous treatment regimen or
        clinical study within 14 days of the first dose of study treatment. Any unresolved
        toxicities from prior therapy greater than Common Terminology Criteria for Adverse Events
        (CTCAE) grade 1 at the time of starting study treatment with the exception of alopecia.
        Presence of life-threatening metastatic visceral disease, uncontrolled central nervous
        system metastatic disease or symptomatic pulmonary lymphangitic spread. Any evidence of
        severe or uncontrolled systemic diseases, including uncontrolled hypertension, active
        bleeding diatheses, or active infection. Unexplained symptomatic endometrial disorders.
        Uncontrolled symptomatic thyroid dysfunction. Inadequate bone marrow reserve or organ
        function