Triptorelin With Either Exemestane or Tamoxifen in Treating Premenopausal Women With Hormone-Responsive Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed breast cancer * Completely resected disease * No clinically detectable residual loco-regional axillary disease * Prior surgery for primary breast cancer of 1 of the following types: * Total mastectomy with or without adjuvant radiotherapy * Breast-conserving procedure (e.g., lumpectomy, quadrantectomy, or partial mastectomy with margins negative\* for invasive disease and ductal carcinoma in situ) with planned radiotherapy NOTE: \*If all other margins are clear a positive posterior (deep) margin is permitted, provided the excision was performed down to the pectoral fascia and all tumor has been removed OR a positive anterior (superficial; abutting skin) margin is allowed provided all tumor was removed * Tumor confined to the breast and axillary nodes * Tumor detected in internal mammary chain nodes by sentinel node procedure and is not enlarged is allowed * Axillary lymph node dissection or a negative axillary sentinel node biopsy required * Patients with negative or microscopically positive axillary sentinel nodes are eligible * Positive sentinel nodes must have either axillary dissection or radiation of axillary nodes * No distant metastases * No locally advanced inoperable breast cancer, including any of the following: * Inflammatory breast cancer * Supraclavicular node involvement * Enlarged internal mammary nodes (unless pathologically negative) * Bilateral synchronous invasive breast cance…