Extended Adjuvant Treatment With Letrozole in Breast Cancer Who Complete 5 Years of Toremifene

Inclusion Criteria: 1. Patients have undergone surgery of the breast cancer and proven histologically to be invasive breast cancer. 2. Removed the breast cancer histologically or cytologically 3. No evidence of breast cancer in controlateral breast 4. No evidence of metastasis 5. Postmenopausal Women With Hormone Receptor Positive Breast Cancer Who Complete 5 Years of Toremifene in 30 months 6. Postmenopausal state was defined the following conditions, at least one of a, b 1. Serum FSH ≥ 30 mIU/mL 2. Amenorrhea ≥ 1 year 7. Estrogen receptor(+) or Progesterone receptor(+) 8. No Evidence of Recurrence Exclusion Criteria: 1. Patient with hormone receptor negative 2. Patients with malignancies 3. Patients with other aromatase inhibitor and chemotherapy 4. Patients with Other hormone therapy and Hormonal replacement therapy 5. Patients with Hormone replacement therapy during taking Toremifene 6. Estimated life expectancy of \<12 months 7. WBC\<3,000/mm3 or Platelet count\<100,000/mm3 8. AST and/or ALT ≥2xUNL 9. Alkaline phosphatase ≥2xUNL