ESR1 and breast cancer: By inhibiting CDK 4/6, palbociclib has a positive effect on the treatment of ER‐positive and HER2‐negative advanced breast cancer.32, 33 Our analysis showed that palbociclib is beneficial in prolonging PFS (HR: 0.518, 95% CI: 0.444‐0.604) in ER‐positive and HER2‐negative breast cancer patients.