CDK4 and breast cancer: Background/Objectives: This meta-analysis aimed to evaluate the efficacy of combining CDK4/6i with ET, compared with ET alone, in improving invasive disease-free survival (iDFS), distant recurrence-free survival (DRFS), and overall survival (OS) in early-stage hormone receptor-positive (HR+), human epidermal growth factor 2-negative (HER2−) breast cancer.