Cyclin-dependent kinase 4 and 6 inhibitors in hormone receptor-positive, human epidermal growth factor receptor-2 negative advanced breast cancer: a meta-analysis of randomized clinical trials

Background Breakthrough progress has been made in Cyclin-Dependent kinase 4 and 6 (CDK4/6) inhibitors when combined with endocrine therapy (ET) for hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC). Though significant improvements of progression-free survival (PFS) for CDK4/6 inhibitors were demonstrated, however, the results of overall survival (OS) profile were not consistent. This study is conducted to further evaluate the efficacy and safety of CDK4/6 inhibitors for HR+ /HER2- ABC, and explore the prefer population through subgroup analysis. Method We identified relevant randomized controlled trials that compared CDK4/6 inhibitors plus ET to ET alone in HR+ /HER2- ABC. We calculated the hazard ratios (HRs) for PFS and OS, and risk ratios (RRs) for objective response rate (ORR), clinical benefit rate (CBR), adverse events (AEs). Statistical analysis was performed with the random-effects model. Result Eight trials and 4580 patients were included in this meta-analysis. Compared to ET alone, CDK4/6 inhibitors plus ET not only produced a significantly longer PFS (HR = 0.55, 95% confidence interval [CI] 0.50-0.59, p < 0.00001), but also manifested an extension of OS (HR = 0.79, 95% CI 0.67-0.93, p = 0.004) for HR+ /HER2- ABC. Similarly, the benefit was also manifested in ORR (RR = 1.47, 95% CI 1.30-1.67, p < 0.00001) and CBR (RR = 1.20, 95% CI 1.12-1.30, p < 0.00001). The improvements of PFS were observed in the combined treatment group as both the first-line (HR = 0.56) and the second-line therapy (HR = 0.53), and irrespective of menopausal status, the presence of visceral metastasis, previous treatment with chemotherapy, their race or age. Nevertheless, more hematologic and gastrointestinal adverse events were observed with CDK4/6 inhibitors. The most common Grade 3-4 AEs is neutropenia (RR 31.95). Conclusion Significant advantages of PFS and OS were observed for CDK4/6 inhibitors in HR+/HER2- ABC. Furthermore, the benefit of PFS was across all subgroups. Though associated with an increased occurrence of AEs, most of which are reversible, manageable, and acceptable. Therefore, CDK4/6 inhibitors could be recommended as a preferred options for patients with HR+ /HER2- ABC.