RATIONALE: Estrogen can stimulate the growth of breast cancer cells. Hormone therapy using tamoxifen may fight breast cancer by blocking the uptake of estrogen. Chemotherapy uses different ways to stop tumor cells from dividing so they stop growing or die.

PURPOSE: Phase III trial to study the effectiveness of tamoxifen following surgery and chemotherapy in treating women who have stage I breast cancer at high risk of recurrence or stage II or stage III breast cancer.

OBJECTIVES: I. Compare the duration of overall survival and disease-free survival in premenopausal women with operable, high risk node negative or axillary node-positive breast cancer who have undergone complete surgical resection of all known disease by means of total or partial mastectomy, and have received standard adjuvant chemotherapy with cyclophosphamide, methotrexate, and fluorouracil (CMF), cyclophosphamide, epirubicin, and fluorouracil (CEF), or doxorubicin and cyclophosphamide (AC) followed by either daily tamoxifen for 5 years or placebo. II. Compare the short- and long-term toxicity in patients receiving tamoxifen versus placebo. III. Monitor follicle-stimulating hormone, luteinizing hormone, and estradiol levels, and determine whether overall survival and disease-free survival are affected by hormonal or menopausal status during or at completion of adjuvant chemotherapy or during or after tamoxifen or placebo treatment in these patients.

OUTLINE: This is a randomized, double blind study. Patients are stratified by adjuvant chemotherapy regimen (cyclophosphamide, epirubicin, and fluorouracil vs cyclophosphamide, methotrexate, and fluorouracil vs cyclophosphamide and doxorubicin), hormone receptor status (ER and/or PR positive vs ER and PR negative), number of positive nodes (1-3 vs 4-9 vs 10 or more), and participating institution. Patients receive one of three regimens of adjuvant chemotherapy at the discretion of the investigator. Regimen A: Patients receive oral cyclophosphamide on days 1-14 and epirubicin IV and fluorouracil IV on days 1 and 8. Courses repeat every 28 days for a total of 6 courses. Following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Regimen B: Patients receive oral cyclophosphamide on days 1-14 or cyclophosphamide IV on day 1 and 8, methotrexate on days 1 and 8, and fluorouracil IV on days 1 and 8. Courses repeat every 28 days for a total of 6 courses. Concurrent with or following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Regimen C: Patients receive doxorubicin IV and cyclophosphamide IV every 21 days for a total of 4 courses. Following chemotherapy, lumpectomy patients receive local radiotherapy daily for 5 weeks. Patients are then randomized to receive either oral tamoxifen or a placebo once daily for 5 years, beginning within 6 weeks of completion of chemotherapy. Treatment continues in the absence of disease progression or unacceptable toxicity. Patients are followed for survival.

PROJECTED ACCRUAL: A total of 800 patients will be accrued for this study over 4 years.

DISEASE CHARACTERISTICS: Adenocarcinoma of the breast with 1 or more histologically proven positive axillary nodes OR Adenocarcinoma of the breast with negative axillary nodes or adverse prognostic factors such that the patient is at high risk for recurrence and node negative lesion is characterized by the following features: Tumor at least 1 cm Poorly differentiated, SBR grade III, or MSBR grade V and/or lymphatic/vascular invasion Pathologic review by experienced breast pathologist recommended if grade is unspecified and lymphatic/vascular invasion is absent Disease considered potentially curable and treated by 1 of the following: Complete surgical removal of the breast plus axillary node dissection Partial surgical removal of the breast plus axillary node dissection, with the intention of giving breast irradiation following completion of an adjuvant chemotherapy regimen Regional nodal or chest wall irradiation not prohibited but strongly discouraged No evidence of residual tumor in the axilla following dissection No microscopic evidence of residual tumor at the resection margins following total mastectomy Further excision highly recommended if there is microscopic residual disease present at partial mastectomy margins If further excision is not undertaken, a radiotherapy boost to the tumor bed is required in addition to breast irradiation given following protocol chemotherapy Disease clinically staged prior to surgery as T1-T3a, N0-2, M0 No clinical T4 disease, i.e.: No extension to the chest wall No edema (including peau d'orange) No skin ulceration No satellite skin nodules confined to the same breast No inflammatory carcinoma Disease pathologically staged following surgery as TNM stage I, II, or III (T0-4; N0-2; M0) T4 allowed only with dermal involvement on pathology assessment No evidence of metastatic disease beyond the homolateral axillary nodes on pre-chemotherapy chest x-ray, bone scan (with radiographs of suspicious areas), and abdominal ultrasound (required only if bilirubin, alkaline phosphatase, or AST/ALT are elevated) Simultaneous bilateral breast carcinoma allowed Complete tumor resection on both breasts required Axillary dissection on both sides must meet criteria as above if both sides are clinically node-positive Axillary dissection on the second side optional if the axilla is clinically negative at the time of surgery and the other side is node-positive Adjuvant chemotherapy must begin within 14 weeks of initial pathologic diagnosis Hormone receptor status: Any receptor level allowed (values must be available if biochemical method used; immunocytochemical assay permitted)

PATIENT CHARACTERISTICS: Age: Not specified Sex: Female Menopausal status: Pre- or perimenopausal, i.e., meeting at least 1 of the following criteria: Normal menstruation Amenorrhea for less than 1 year (up to 3 years in patients under age 52) Biochemical evidence of ovarian function Hysterectomy without bilateral oophorectomy in patients under age 56 Premenopausal women no greater than age 50 who were started on replacement hormone therapy before amenorrhea are eligible Performance status: ECOG 0-2 prior to chemotherapy Hematopoietic: WBC at least 3,000/mm3 Polymorphs and bands at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: (unless abdominal ultrasound indicates liver metastasis) Alkaline phosphatase no greater than 2 times normal AST and/or ALT no greater than 2 times normal Renal: Not specified Other: No history of serious underlying medical illness or psychiatric or addictive disorder No second malignancy within 5 years except: Curatively treated nonmelanomatous skin cancer Curatively treated endometrium, colon, or thyroid cancer or carcinoma in situ of the cervix No plan for pregnancy during the 5-year study period Fertile women must use effective contraception (other than oral contraception) Accessible for treatment and follow-up

PRIOR CONCURRENT THERAPY: Biologic therapy: Colony-stimulating factors allowed (use must be documented) Chemotherapy: No prior chemotherapy No concurrent other cytotoxic therapy Endocrine therapy: Adjuvant tamoxifen (20 mg po daily) allowed up to 2 weeks before or during adjuvant chemotherapy provided drug is discontinued at randomization No long-term prednisone or other hormones Radiotherapy: See Disease Characteristics Surgery: See Disease Characteristics