NeoTAILOR: ABiomarker-directed Approach to Guide Neoadjuvant Therapy for Patients With Stage II/III ER-positive, HER2-negative Breast Cancer

Risk category is defined as follows: * Low risk: * Baseline Ki67 ≤ 10% (OR) * Luminal A molecular intrinsic subtype by PAM50 * High risk: * Non-Luminal A molecular intrinsic subtype by PAM50 (OR) * In cases of non-diagnostic PAM50 molecular intrinsic subtype, patients will enroll in the high-risk group and undergo Week 4 tumor biopsy.