Evaluating the Addition of Adjuvant Chemotherapy to Ovarian Function Suppression Plus Endocrine Therapy in Premenopausal Patients With pN0-1, ER-Positive/HER2-Negative Breast Cancer and an Oncotype Recurrence Score Less Than or Equal to 25

Inclusion Criteria: * A patient cannot be considered eligible for this study unless ALL of the following conditions are met. * The patient or a legally authorized representative must provide study-specific informed consent prior to pre-entry and, for patients treated in the U.S., authorization permitting release of personal health information. * Female patients must be greater than or equal to 18 years of age. * Patients must be premenopausal (evidence of functioning ovaries) at the time of pre-entry. For study purposes, premenopausal is defined as: * Age 50 years or under with spontaneous menses within 12 months; or * Age greater than 50-60 years with spontaneous menses within 12 months plus follicle-stimulating hormone (FSH) and estradiol levels in the premenopausal range; or * Patients with amenorrhea due to IUD or prior uterine ablation must have FSH and estradiol levels in the premenopausal range; or * Patients with prior hysterectomy must have FSH and estradiol levels in the premenopausal range. * The patient must have an ECOG performance status of less than or equal to 2 (or Karnofsky greater than or equal to 60%). * Patients may have ipsilateral or contralateral synchronous breast cancer if the highest stage tumor meets entry criteria, and the other sites of disease would not require chemotherapy or HER2-directed therapy. * Patients may have multicentric or multifocal breast cancer if the highest stage tumor meets entry criteria, and the other si…