Inclusion Criteria:

1. Written signed informed consent.

2. Breast cancer histologically confirmed.

3. Stages I, II, IIIA of invasive breast cancer. Patients must comply with one of the
following characteristics: N+, T > 2 cm.

4. Mastectomy or lumpectomy with free margins + radiotherapy, axilar node dissection or
centinel node dissection.

5. Positive hormonal receptors (ER+ and/or PgR+) determined at a central laboratory.

6. Negative HER2 (defined as IHQ 0 or 1+ or negative FISH when IHQ 2+ or 3+).

7. Postmenopausal women (woman complies with one of the following criteria: age ≥ 60
years, age ≥ 45 years and amenorrhea, amenorrhea ≥ 12 months and undamaged uterus,
bilateral ovariectomy, FSH and estradiol level into postmenopausal range (using local
ranges).

8. ECOG = 0, 1 or 2.

9. Age > 18 years.

Exclusion Criteria:

1. Metastatic disease or invasive bilateral breast cancer.

2. Negative ER and PgR breast cancer.

3. Treatment with a not approved or experimental drug within 4 weeks before
randomization.

4. Current or previous malignant process within the last 5 years (different from breast
cancer or basocelular carcinoma or escamocelular of the skin or cervix carcinoma in
situ).

5. Pregnant or lactating women. 6. Concurrent hormone replacement therapy and other
hormonal agents (raloxifen, tamoxifen,etc.)