To explore the relative contributions of proliferative arrest and cell death underlying the activity of INX-315 in CDK4/6i–resistant breast cancer, we treated parental cells with abemaciclib or INX-315 and treated resistant cells (cultured in drug(s) to which they were resistant) with INX-315 prior to measuring indices of proliferation and apoptosis. This evidence concerns the gene CDK4 and breast carcinoma.