Inclusion Criteria:

- Provision of written informed consent

- Patients with early breast cancer who are scheduled to receive first-line adjuvant
endocrine therapy with aromatase inhibitor under the routine clinical practice

- Histologically or cytologically proven to be HR+(ER or PR +)

- Postmenopausal woman, defined as a woman fulfilling any of the following criteria(by
the local guideline):

- Age >= 50 years

- Age < 50 years with amenorrhoea > 12 months and an intact uterus

- FSH levels within postmenopausal range (over 30-40 IU/ml), or

- Having undergone a bilateral oophorectomy.

- No other concomitant endocrine therapy such as estrogen therapy or selective
estrogen receptor modulators

Exclusion Criteria:

- Recurrence of breast cancer

- Known hypersensitivity to aromatase inhibitor or to any of the excipients

- Any severe concomitant condition which makes it undesirable for the patient to
participate in the trial or which would jeopardize compliance with the trial protocol

- Previous inclusion in the present study

- Participation in a clinical study during the last 30 days