To further explore what molecules were involved in the development of CDK4/6i resistance, we analyzed genomic alterations in 348 ER + breast cancers treated with CDK4/6i from the open literature published in 2018 CancerCells [15] and found that the protein and RNA of PARP1 were upregulated in some patients (Fig. 1A). Here, CDK4 is linked to breast cancer.