Elacestrant vs Standard Therapy for Early Breast Cancer

Key Inclusion Criteria: * Histopathologically or cytologically confirmed ER+ (≥10% by immunohistochemistry \[IHC\]), HER2- (tumors with an IHC score of 0, 1+, or 2+ with in situ hybridization \[ISH\]-negative \[not amplified\]). ISH-negative without IHC testing will also be eligible on tumor biopsy or final surgical pathology specimen early stage resected invasive breast cancer without evidence of recurrence or distant metastases, per local laboratory, according to the American Society of Clinical Oncology/College of American Pathologists guidelines. * Participants must be node positive (microscopic and macroscopic tumor involvement are allowed) and fulfill one of the following criteria: 1. ≥4 positive axillary lymph nodes or 2. 1-3 positive axillary lymph nodes and 1. Histologic grade 3 disease and/or 2. Tumor size ≥5 centimeters and/or 3. High genomic risk (identified by Oncotype, MammaPrint, EndoPredict, PAM50) * Participants who are currently taking endocrine therapy (aromatase inhibitors or tamoxifen) and have received at least 24 months but not more than 60 months of endocrine therapy at the time of randomization (Cycle 1 Day 1 \[C1D1\]) with or without a CDK 4 and CKD 6 inhibitor (CDK4/6i) and with or without a luteinizing hormone-releasing hormone agonist. * Participants who received prior CDK4/6i or a poly adenosine diphosphate-ribose polymerase inhibitor must have already completed or discontinued these treatments. Key Exclusion Criteria: * Participants with inflammatory breast cancer. * History of any prior (ipsilateral and/or contralateral) invasive breast cancer. * Participant with history of non-breast malignancy within 3 years of the date of randomization, except for adequately treated basal or squamous cell skin cancer, superficial bladder cancer or carcinoma in situ of the cervix. * Participants who have had more than a 6-month continuous interruption of prior SoC adjuvant endocrine therapy or who are off current adjuvant endocrine therapy more than 6 months prior to randomization. Note: Other protocol defined Inclusion/Exclusion criteria may apply.