Arimidex: Compliance and Arthralgias in Clinical Therapy (COMPACT)

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