CDK4 and breast cancer: Addition of immune checkpoint inhibitors (PD-1and CTLA-4) to CDK4/6 inhibitors holds promise by inhibiting the growth and proliferation of cancerous cells and, with this study as the background, a clinical trial (JPCE) has focused on studying the suitability and efficacy of using abemaciclib in combination with pembrolizumab in HR+/HER-2 negative metastatic BC patients (253).