ESR1 and breast cancer: The study “Multigene Risk Score Combined with Ki-67 Dynamic Assessment in Stratified Neoadjuvant Endocrine Therapy Treatment With or Without CDK4/6 inhibitors in ER+/HER2- Breast Cancer” evaluates the efficacy of the neoadjuvant CDk4/6 inhibitor dalpiciclib in high-risk EPclin and non-ET responders (defined as no decrease in Ki67 levels after two weeks of Letrozole).