Inclusion Criteria:

- Provision of informed consent.

- Age ≥ 40 years.

- Female patients with ER-positive early breast cancer, who receive therapy with a
third generation AI either as first line hormonal treatment or as maintenance therapy
after first-line anthracycline- and/or taxane-based chemotherapy for a period no
longer than 1 month (4 weeks) prior to inclusion in the present study.

- Women who have been rendered postmenopausal prior to chemotherapy commencement and at
least 12 months from last menstrual period. For subjects who are amenorrheic for < 12
months (including patients who underwent hysterectomy, or received ERT/HRT), they
must have serum FSH ≥50 UI/L before the commencement of AI therapy.

- Patients with available data on lumbar spine and total hip BMD prior to chemotherapy
initiation as well as before the commencement of AI therapy.

Exclusion Criteria:

- Prior administration of other endocrine therapy including tamoxifen.

- Chemotherapy-induced menopause.

- Evidence of diseases known to interfere with bone metabolism, such as
hyperparathyroidism, hyperthyroidism, osteomalacia, chronic liver disease, renal
failure, hypercortisolism, malabsorption, and immobilization.

- Evidence of bone metastasis or evidence of abnormal clinical laboratory parameters
that are assessed as clinically significant by the investigator.

- Involvement in the planning and conduct of the study.

- Participation in other clinical study within a period of 3 months prior to any study
related procedures.

- Patients with normal bone density or mild osteopenia (T score >= -2 in any site)
under treatment with oral or intravenous bisphosphonates. Vitamin D and calcium
supplements are allowed.

- Patients with severe osteopenia or osteoporosis (T score <= -2 in any site) under
treatment with intravenous bisphosphonates. Oral bisphosphonates, Vitamin D and
calcium supplements are allowed.

- Patients under treatment with oral or intravenous bisphosphonates before chemotherapy
commencement.

- Patients that stopped hormone-replacement therapy (HRT) less than 3 months before
chemotherapy commencement.

- Patients that received neo-adjuvant treatment.