ERBB2 and breast cancer: Another meta-analysis investigated the efficacy and safety of CDK4/6 and PI3K/AKT/mTOR inhibitors as second-line treatment in postmenopausal patients with HR+/HER2- metastatic BC [24] and revealed no statistical differences between three combinations of three CDK4/6 inhibitors with fulvestrant regarding PFS and OS, which was consistent with our findings.