The purpose of this study is to determine the efficacy and tolerability of 3 years treatment with anastrozole after a prior 2 years' treatment with tamoxifen versus 5 years treatment with tamoxifen in postmenopausal women with early breast cancer

Inclusion Criteria:

• Signed informed consent,
• Post-menopausal women ≤75 years,
• histologically confirmed invasive breast carcinoma (no distant metastases),
• positive hormone receptor status,
• continuous 2-year adjuvant tamoxifen therapy 20 mg/30 mg with 4 weeks after primary surgery

Exclusion Criteria:

• menopause status maintained by medication,
• pre-operative chemotherapy or hormone therapy or radiation therapy,
• relapse or second carcinoma or previous cancerous disease,
• breast carcinoma in situ,
• simultaneous carcinoma of the opposite side or secondary breast,
• 10 or more tumour-infiltrated lymph nodes.
• serious accompanying diseases