The purpose of this study is to identify the combined impact on bone loss as well as the incidence of bone fractures in women with estrogen receptor (ER)-positive, early breast cancer treated with an aromatase inhibitor (AI) either as first line therapy or as maintenance therapy after initial treatment with chemotherapy, in real life clinical settings in Greece.

Subjects with ER-positive early breast cancer will be treated with AIs either as first line therapy or as maintenance therapy after initial treatment with chemotherapy. The total study duration will be 24 months comprising of a recruitment period of 12 months and a follow-up period of 12 months for each participating subject. The primary outcome variable is the mean percentage variation in lumbar spine (LS) bone mineral density (BMD) during the 12 month follow - up period. Measurements will be taken before and after chemotherapy and at the end of the 12 month follow - up period.

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 estrogen replacement therapy (ERT)/ hormone replacement therapy (HRT), they must have serum follicle stimulating hormone (FSH) ≥50 IU/L before the commencement of AI therapy.
• Patients with available data on lumbar spine and total hip bone mineral density (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.

Post-menopausal 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 study