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OBJECTIVE: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) have been recommended as standard therapeutic strategies for hormone receptor-positive (HR+), human epidermal growth factor receptor type 2-negative (Her2-) advanced breast cancer (ABC). While the benefits to progression-free survival (PFS) rates have been confirmed, whether the combination of CDK4/6i and ET leads to overall survival (OS) rate improvements remains controversial. This study aimed to assess the long-term efficacy and safety of CDK4/6i in HR+, Her2- ABC patients and identify a population suitable for treatment with CDK4/6i by subgroup analysis. MATERIALS AND METHODS: Electronic literature databases (MEDLINE, EMBASE and the Cochrane Library) were searched for relevant randomized controlled trials (rcts) published from Jan 2014 to Jan 2020. In addition, abstracts and presentations from all major conference proceedings were reviewed. All rcts that compared the efficacy and safety of CDK4/6i plus ET with ET alone in HR+, Her2- ABC patients were selected. The pooled analyses of hazard ratios (hrs) for PFS and OS, and risk ratios (rrs) for the objective response rate (ORR) and adverse events (aes) were obtained with the random-effects model. RESULTS: A total of 6 rcts and 3421 HR+, Her2-ABC patients were enrolled for OS outcome analysis, while all 8 trials and 4580 patients were included for PFS outcome analysis. The pooled hrs for the OS and PFS were 0.76 (95% CI: 0.670.84) and 0.55 (95% CI: 0.50-0.59), respectively, and were consistent in the subgroup analysis. Moreover, CDK4/6i meaningfully improved the ORR in both the intention-to-treat population (RR=1.47; 95% CI: 1.29-1.67) and patients with measurable disease (RR=1.47; 95% CI: 1.301.67); however, CDK4/6i increased the incidence of grade 3/4 aes (RR=2.69; 95% CI: 2.43-2.97). CONCLUSIONS: The combination of CDK4/6i and ET was superior to ET alone in terms of OS and PFS regardless of the drugs administered, the treatment line, age distribution, race, PR status, menopausal status, metastasis site and endocrine resistance status. [ABSTRACT FROM AUTHOR]