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. The gene discussed is CDK4; the disease is Decreased total leukocyte count.