Treatment consequence and adverse events of cyclin-dependent kinase 4/6 inhibitors on patients with hormone receptor-positive, HER2-negative metastatic breast cancer: a systematic review and meta-analysis.

Although some studies have indicated that CDK4/6 inhibitors are beneficial for the progression-free survival (PFS) and overall survival (OS) in breast cancer, evidence regarding the assessment of clinical response remains insufficient. Therefore, this study aims not only to evaluate the efficacy and safety of CDK4/6 inhibitors combined with endocrine therapy in HR(+)/HER2(-) metastatic breast cancer, but also to analyze the objective response rate (ORR) and clinical benefit rate (CBR), providing comprehensive clinical outcome insights. A literature search was performed in PubMed, Embase, Cochrane Library, and ClinicalTrials.gov focusing on studies published before 2022. The meta-analysis followed PRISMA guidelines and used RevMan 5.3 to conduct the analysis. Eleven clinical trials published between 2015 and 2022 were included in our meta-analysis, with a total of 5572 eligible patients. This meta-analysis found that HR(+)/HER2(-) metastatic breast cancer treated with CDK4/6 inhibitors plus endocrine therapy can significantly improve progression-free survival(PFS) (HR: 0.55; p < 0.001), overall survival (OS) (HR: 0.79; p < 0.001), objective response rate (RR = 1.50; p < 0.001), clinical benefit rate (RR = 1.18; p < 0.001) and decrease progressive disease rate (RR = 0.49; p < 0.001). Clinicians need to be aware of hematological toxicities, abnormal liver function, and venous thromboembolism in the use of CDK4/6 inhibitors. Furthermore, the combination regimen also showed longer PFS in subgroup analysis. However, Asians, the number of metastasis sites, and patients using letrozole subgroups did not demonstrate differences in OS between the combination regimen and endocrine therapy alone. This meta-analysis highlights the improvement of PFS, OS, ORR, and CBR in HR(+)/HER2(-) metastatic breast cancer for CDK4/6 inhibitors, with manageable and reversible toxicities. Clinicians should be aware of hematological toxicities, liver function abnormalities, and venous thromboembolism when using CDK4/6 inhibitors. These findings make CDK4/6 inhibitors a pivotal treatment option.