Efficacy of CDK4/6 Inhibitor Plus Aromatase Inhibitor versus Fulvestrant in Chinese Patients with Hormone...

The multicenter, real-world study aims to explore the clinical efficacy of the cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) plus aromatase inhibitor (AI) versus fulvestrant (FUL) in Chinese patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC).

We retrospectively collected clinicopathological data of cancer patients receiving CDK4/6i from four cancer centers in China. Clinical benefit rate (CBR), objective response rate (ORR), and progression-free survival (PFS) were compared between AI- and FUL-combined therapy.

A total of 315 patients with HR+/HER2- ABC were qualified. 188 (59.7%) patients received AI+CDK4/6i, and 127 (40.3%) patients received FUL+CDK4/6i therapy. In the overall population, the median PFS was 16.8 months versus 14.9 months for AI+CDK4/6i and FUL+CDK4/6i (p=0.34, HR=0.87, 95% CI=0.64-1.17). ORR (19.7% versus 24.4%, p=0.33) and CBR (69.7% versus 77.2%, p=0.16) were comparable between the two treatment regimens. For patients receiving post-first-line (1L) therapy, CBR for FUL+CDK4/6i therapy was 69.1%, which was significantly higher than 52.6% for AI+CDK4/6i therapy (p=0.04). Among ET-resistant subgroups, FUL+CDK4/6i achieved a higher CBR of 70.1% compared with 56.2% for AI+CDK4/6i (p = 0.008). In other subgroups, including patients receiving 1L CDK4/6i, who had a favorable response to ET, with/without liver metastasis at first relapse, the median PFS, ORR, and CBR showed no statistical difference (all p>0.05).

In general, both AI and FUL combinations are effective alternatives, irrespective of the CDK4/6i treatment line, liver metastasis at first relapse, or endocrine sensitivity. Further studies are expected.