CDK4 and breast cancer: <b>Results:</b> Our analysis included 24 meta-analyses systematic reviews that evaluated the quality of AEs in 13 cases of early breast cancer (EBC) and 158 cases of advanced breast cancer The addition of CDK4/6 inhibitors was found to significantly increase AEs of any grade and AEs of grade 3 or higher in early breast cancer, along with a significant increase in the risk of treatment discontinuation.