Patients are eligible for inclusion in this NIS if they have taken anastrozole either upfront or following two to three years of tamoxifen treatment ("switch") for at least three and not more than six months prior to offering an individual participation in this program. Treatment should follow local therapy guidelines and standard practice. Treatment decisions for patients participating in this study including assessments or supportive therapy during follow-up visits will also follow guidelines and remain independent of the program.

The patient population will include postmenopausal women with hormone-receptor positive primary breast cancer scheduled for adjuvant upfront endocrine treatment with anastrozole or following two to three years of tamoxifen treatment ("switch") according to the current SmPC (Appendix C). Patients will have taken anastrozole for at least three months and not more than six months before the start of the study.

Inclusion Criteria:

• Postmenopausal women aged 18 years or older; Postmenopause is defined as Natural menopause with menses >1 year ago or Serum FSH (> 20 IU/ l), and E2 levels in the postmenopausal range or patients who had bilateral oophorectomy
• Histologically / cytologically confirmed primary diagnosis of early breast cancer (M0) with hormone sensitive tumour (ER+ve and/or PgR+ve)
• Patients, who underwent breast cancer surgery and, if appl. radiation therapy and/or neo/adjuvant chemotherapy and have taken adjuvant endocrine treatment with anastrozole (upfront or following two to three years of tamoxifen) min 3 max 6 months
• In case of a previous therapy with tamoxifen (switch-therapy), duration of tamoxifen treatment for at least two and up to three years.

Exclusion Criteria:

• Patients with severe renal function disorders (Creatinine clearance < 20 ml/min or Patients with moderate or severe disorders of hepatic function
• Concomitant treatment with drugs known to affect sex hormonal status and tamoxifen
• Patients with ductal carcinoma in situ (DCIS) without primary diagnosis of early breast cancer (M0)
• Evidence of any significant clinical disorder or laboratory finding which in the opinion of the investigator, makes it undesirable for the patient to participate in the program

The patient population will include postmenopausal women with hormone-receptor positive primary breast cancer receiving adjuvant endocrine treatment with anastrozole upfront or following two to three years of tamoxifen therapy ("switch") according to the current SmPC (Appendix C). Patients will have received anastrozole treatment for at least 3 months and up to 6 months before the start of the study.