CDK4 and neutropenia: The most common adverse reactions associated with CDK4/6i (≥20% with any CDK4/6i in first-line trials in combination with a nonsteroidal AI and greater than placebo) are shown in Figure 4, and notably include blood cell count abnormalities (i.e., neutropenia, leukopenia, anemia), abnormal liver functions tests, and diarrhea.