PRIOR CONCURRENT THERAPY: No concurrent participation in another adjuvant breast cancer trial that has disease-free or overall survival as a study endpoint (e.g., a major cooperative group trial) Biologic therapy: Not specified Chemotherapy: Concurrent adjuvant cyclophosphamide, methotrexate, fluorouracil (CMF), doxorubicin, cyclophosphamide (AC), AC followed by paclitaxel, or fluorouracil/doxorubicin/cyclophosphamide (FAC, CAF) allowed If ER negative, approved chemotherapy regimen and/or tamoxifen required No more than 120 days between definitive surgery and initiation of adjuvant systemic chemotherapy Endocrine therapy: Concurrent adjuvant tamoxifen required if ER positive (if ER negative, tamoxifen and/or an approved chemotherapy regimen required) No more than 180 days between definitive surgery and initiation of tamoxifen (if receiving tamoxifen alone) If receiving adjuvant CMF, AC, or FAC, CAF, or AC, paclitaxel, tamoxifen begins after completion of adjuvant therapy Radiotherapy: Radiotherapy required within 56 days following segmental mastectomy Surgery: Definitive surgery required Prior oophorectomy for reasons other than malignancy allowed