ESR1 and breast carcinoma: The “Neoadjuvant Dose-dense Chemotherapy for HR+/HER2- Breast Cancer Patients With High Proliferation Index” study uses a high proliferation index score (Ki67 > 30%) to select high-risk ER+/HER-2- patients as candidates for neoadjuvant treatment with dose-dense paclitaxel followed by epirubicin cyclophosphamide.