- Prior therapy for breast cancer, including irradiation, chemotherapy, biotherapy, and/or hormonal therapy, with the exception of tamoxifen. Tamoxifen may be given as adjuvant therapy before study entry, but only if it was started within 28 days before randomization. Patients who started tamoxifen within 28 days before randomization and who are being considered for chemotherapy must have their tamoxifen stopped at the start of chemotherapy.