CDK4 and breast cancer: Otherwise, in the single-arm phase II ELAINE 2 trial, among 29 women with HR + /HER2− ESR1-mutated metastatic BC (MBC) whose disease progressed after 1–2 prior lines of ET with or without CDK4/6i, lasofoxifene plus abemaciclib was well-tolerated and demonstrated activity with median PFS (mPFS) of 13.9 months and objective response rate (ORR) of 33.3%31.