CDK4 and breast cancer: A recent meta-analysis confirmed that the combination of CDK4/6 inhibitors and endocrine treatment achieves a significantly improved PFS (hazard ratio (HR) 0.54, 95% confidence interval (CI) 0.50–0.59, p < 0.00001) and OS (HR 0.77, 95% CI 0.69–0.85, p < 0.00001) compared with endocrine therapy alone in HR-positive, HER2-negative advanced breast cancer [12].