Objective To compare the efficacy and safety of different cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) for the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2?) advanced or metastatic breast cancer. Methods Randomized controlled trials (RCTs) on CDK4/6i for the treatment of HR+/HER2? metastatic or advanced breast cancer were retrieved from databases including PubMed, EMbase, Web of Science, The Cochrane Library, CNKI, Wanfang, VIP, and SinoMed, with the search period ranging from database inception to August 2023. Bayesian network meta-analysis was conducted using R 4.2.0 software. Results A total of 18 RCTs from 25 articles, involving 8 031 patients and 11 treatment regimens, were included. There was no significant difference in progression-free survival (PFS) or overall survival (OS) among different CDK4/6i+ET combinations. The highest cumulative probability for PFS was observed with dalpiciclib (DAL)+fulvestrant (FUL), while ribociclib (RIB)+FUL ranked first for OS. In terms of efficacy, abemaciclib (ABE)+aromatase inhibitors (AI) and ABE+FUL ranked first in objective response rate and clinical benefit rate, respectively. Regarding safety, statistically significant difference in grade 3-4 adverse events was observed among certain types of CDK4/6i (P<0.05). Conclusion Current evidence suggests that CDK4/6i+ET is superior to ET alone for the treatment of HR+/HER2? advanced/metastatic breast cancer. Different CDK4/6i+ET combinations demonstrate comparable or similar efficacy; however, the incidence of adverse reactions is higher with combination therapy. Treatment regimens should be selected based on individual conditions.
