Inclusion Criteria:

- Histological or cytological diagnosis of breast cancer

- Postmenopausal status at the time of enrolment, according to the following
definitions:

- History of bilateral oophorectomy at any age

- Proven hormonal menopause

- Positive estrogen receptor (ER) and/or progesterone receptor (PR) by immuno

- Failure of one previous endocrine therapy in the adjuvant or metastatic setting

- Use of no more than one previous chemotherapy regimen in the neoadjuvant or adjuvant
setting

- Indication to receive chemotherapy or endocrine therapy

Exclusion Criteria:

- Inability to comply with the study protocol

- Use of more than one previous endocrine therapy, regardless of the setting; --
Previous use of chemotherapy for metastatic disease

- Use of neoadjuvant endocrine therapy as the only previous type of endocrine therapy

- Serious medical, surgical or psychiatric comorbidity that, upon investigator's
discretion, should preclude participation in the study.