RATIONALE: Estrogen can stimulate the growth of breast cancer cells. Hormone therapy using tamoxifen may fight breast cancer by blocking the uptake of estrogen.

PURPOSE: Phase III trial to compare the effectiveness of adjuvant therapy using tamoxifen or ovarian ablation with goserelin or both in treating women with stage I or stage II breast cancer.

OBJECTIVES: I. Determine, in a prospective, randomized, controlled trial whether the administration of a course of adjuvant tamoxifen or ablation of ovarian function results in prolongation of time to recurrence or death in patients under 50 years of age with operable carcinoma of the breast. II. Determine how hormone manipulation affects mood and sexual functioning in these patients.

OUTLINE: This is a randomized study. Patients are stratified by clinician. All patients are randomized following primary therapy, which, in addition to surgery, may include local irradiation, perioperative cyclophosphamide, or up to 6 cycles of cyclophosphamide, methotrexate, and fluorouracil (CMF) for high-risk patients. Clinicians may elect to randomize patients to all groups or to only those groups including tamoxifen. The first group receives no further therapy. Then second group receives tamoxifen daily for at least 2 years. The third group receives ovarian ablation with goserelin via monthly injection for at least 2 years. The final group receives ovarian ablation with goserelin plus daily tamoxifen for at least 2 years. All patients are followed every 3 months for 2 years, every 6 months for 3 years, then annually.

PROJECTED ACCRUAL: 800 to 1,000 patients will be entered.

DISEASE CHARACTERISTICS: Operable, clinical Stage I/II breast cancer (T1-3, N0-1, M0) No evidence of distant metastases on x-ray of chest, spine, and pelvis Bone scan evidence alone of secondary mass allowed unless considered unequivocal evidence of metastasis No primary carcinoma fixed to underlying muscle or chest wall No deeply fixed axillary nodes No ulceration, skin infiltration, or peau d'orange involving more than 1/3 of breast No bilateral tumors Hormone receptor status: Not specified

PATIENT CHARACTERISTICS: Age: Under 50 Sex: Women only Menopausal status: Any status Performance status: Not specified Life expectancy: No limits on life expectancy due to intercurrent illness Hematopoietic: WBC at least 3,000 Platelets at least 90,000 Hemoglobin at least 10 g/dL Hepatic: Normal liver function required Renal: Normal kidney function required Other: Fit for surgery No prior treatment for other malignancies except: Nonmelanomatous skin cancer Cone-biopsied in situ carcinoma of the cervix English-speaking patients eligible for quality-of-life assessments

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Chemotherapy for high-risk patients allowed at the discretion of the clinician Endocrine therapy: At least 6 weeks since prior hormonal therapy No concomitant hormonal therapy including oral contraceptives (patients must discontinue the pill for 2 years) Radiotherapy: Not specified Surgery: Not specified