To compare the overall QoL (Quality of Life) using Trial Outcome index (TOI) of FACT-B questionnaire for 3 years from baseline.

1. TOI is the sum of the scores from the physical and functional well-being and the breast cancer subscales.
2. To assess incidence of adverse events (including cardiovascular, cerebrovascular, and endocrine, musculoskeletal) in Korean postmenopausal breast cancer patients in early adjuvant setting.
3. To assess the effect of letrozole (Femara) on BMD in early adjuvant setting.
4. To assess the effect of letrozole (Femara) on total cholesterol in early adjuvant setting.

Inclusion Criteria:

1. Patients have undergone surgery of the breast cancer and proven histologically to be breast cancer with postmenopausal women older than 45 years. Postmenopausal state was defined the following conditions, at least one of a, b, c.

   1. serum FSH ≥ 30 mIU/mL
   2. amenorrhea ≥ 1 year
   3. oophorectomy

2. patients with estrogen receptor(+) and/or progesterone receptor(+)

3. WHO(ECOG) performance status 0-2

4. Adequate haematological function, renal function, hepatologic function.

5. No evidence of metastasis.

Exclusion Criteria:

1. patient with hormone receptor negative.
2. Patients with malignancies (other than breast cancer) within the last 5 years, except for adequately treated in situ carcinoma of the cervix or basal cell / squamous cell carcinoma of the skin.
3. Other hormone therapy given within the previous 4 weeks.
4. Patients with other aromatase inhibitor and chemotherapy
5. Uncontrolled infection, medically uncontrollable heart disease
6. Other serious medical illness or prior malignancies
7. Patients with BMD T-score ≤-2.5
8. Patients who were treated with bisphosphonate
9. Patients with postmenopausal state induced chemotherapy
10. Estimated life expectancy of <12 months

Patients recruited into the study are postmenopausal women who had undergone surgery for primary breast cancer which was either estrogen receptor(ER) and/or progesteron receptor(PgR)-positive or of both.