RecruitingPhase 2Drug trialFulvestrant+Abemaciclib With Run-In of Fulvestrant in Er-Positive, Her2-Negative Metastatic Breast CancerThe study will investigate if CDK4/6 inhibitor holiday will reset the cell cycle process to respond to the combination of fulvestrant and abemaciclib, and this approach may represent an effective therapeutic strategy to manage such patients.