The addition of CDK4/6 inhibitors to treatment regimens was associated with a high risk of increased rates of neutropenia, leukopenia, and diarrhea, 3 grade 3/4 AEs that should be considered when treatment periods are long.2 Neutropenia, leukopenia, and diarrhea were the most common symptoms observed among patients who received CDK4/6 inhibitors plus ET treatment of metastatic breast cancer, with diarrhea being the most frequent nonhematologic grade 3/4 AE.36,39 However, those grade 3/4 AEs may be controlled through experience, medication, or dose adjustment. This evidence concerns the gene CDK4 and Decreased total leukocyte count.