OUTLINE: This is a randomized study. Patients are stratified by age and by participating institution. All patients undergo surgical resection with local radiation therapy, as appropriate. Within 4 weeks of surgery, patients receive cyclophosphamide, methotrexate, and fluorouracil (CMF) every 3 weeks for 6 courses. Radiotherapy is given within 4 weeks of completion of CMF. Before beginning the last course of CMF, patients are randomized to receive either oral tamoxifen daily for 5 years or no further therapy. Patients are followed every 6 months for 5 years, then yearly. Hormone therapy is prohibited except as specified above and except for short-term hormone replacement therapy for severe unresponsive menopausal symptoms.