EIF4EBP1 and breast carcinoma: While evaluating the effects of CDK4/6 inhibitors on growth and proliferative signaling pathways, we noticed that, intriguingly, abemaciclib treatment rapidly suppressed S6 and 4EBP1 phosphorylation in several cell lines, including DMS-53 small cell lung cancer (SCLC) and MDA-MB-175 breast cancer cells (Figure 1A, Supplementary Figure 1A, 1B).