Inclusion Criteria:

          1. Histologically or cytologically diagnosis of breast cancer;

          2. Presence of metastatic disease either measureable or non-measureable but evaluable
             bone disease as defined by the Response Evaluation Criteria in Solid Tumors;

          3. Diagnosis of hormone receptor positive (HR+), HER2 negative breast cancer. To fulfill
             the requirement for HR+ disease, a breast cancer must express, by immunohistochemistry
             (IHC), at least one of the hormone receptors (estrogen receptor [ER], progesterone
             receptor [PR]). To fulfill the requirement for HER2 negative disease, a breast cancer
             must not demonstrate over-expression of HER2 by either IHC or fluorescence in-situ
             hybridization (FISH);

          4. Post-menopausal status at the time of randomization.

          5. Previous treatment with either an antiestrogen or an aromatase inhibitor for adjuvant
             or metastatic disease is allowed;

          6. Age >18;

          7. One line chemotherapy for metastatic disease discontinued for 21-28 days. Patient has
             to have response or stability from the first-line chemotherapy. The patient may have
             received prior systemic chemotherapy in the neo-adjuvant or adjuvant setting;

          8. Patients with measurable or evaluable disease according to Response Evaluation
             Criteria in Solid Tumors (RECIST) criteria;

          9. Performance Status (ECOG) <2;

         10. No brain metastases;

         11. No clinically serious concurrent illnesses;

         12. Adequate organ function

         13. Use of bisphosphonates are allowed;

         14. Use of antiangiogenetic drugs (bevacizumab associated to paclitaxel) is allowed, but
             discontinued 21-28 days before start study;

         15. Life expectancy > 12 weeks;

         16. Are willing to participate for the duration of the study and to follow study
             procedures;

         17. Written informed consent prior to any study-specific procedures Written informed
             consent;

        Exclusion Criteria:

          1. Treatment with a drug that has not received regulatory approval for any indication
             within 21-28 days from the randomization;

          2. Drug (chemotherapy or biological drug) after the end of first-line chemotherapy for
             maintenance phase;

          3. Significant known cardiovascular impairment (NYHA CHF > grade 2, unstable angina,
             myocardial infarction within the previous 6 months prior to randomization, or existing
             serious cardiac arrhythmia). VECF (Ventricular Ejection Cardiac Fraction) ≤ 50%;

          4. Prior malignancy (other than breast cancer) except for non-melanoma skin cancer and
             carcinoma in situ (of the cervix or bladder), unless diagnosed and definitively
             treated more than 5 years prior to randomization;

          5. Severe/uncontrolled intercurrent illness within the previous 28 days prior to
             randomization.

          6. Any other significant co-morbid conditions that in the opinion of the Investigator
             would impair study participation or cooperation;

          7. Patients with psychiatric illness, social situation or geographical situation that
             would preclude informed consent or limit compliance with study requirements, as
             determined by the Investigator;