Germline BRCA Mutation Affect the Clinical Outcomes of Metastatic Breast Cancer Treated with CDK4/6 Inhibitor: A Real-world Study

Few clinical studies pay attention to clinical outcomes of CDK4/6 inhibitor in metastatic breast cancer with germline BRCA mutation. The present study aimed to explore whether germline BRCA mutation will affect the clinical efficacy of CDK4/6 inhibitor for metastatic breast cancer. Patients with HR+/HER-2- metastatic breast cancer who were treated with CDK4/6 inhibitor from January 2019 to December 2022 were retrospectively analyzed. Genetic testing of BRCA mutation was performed on next generation sequencing (NGS) platform. The primary end point was progression free survival (PFS). Secondary end points included objective response rate (ORR), disease control rate (DCR), and overall survival(OS). Of the 62 HR+/HER2- metastatic breast cancer patients receiving CDK4/6 inhibitor, gBRCA mutation were detected in 6 patients, 40 patients were gBRCA wt and 16 patients with unknown gBRCA status. Even though there was no statistical difference, the median PFS (9.2m vs. 18.5m vs. 14.1m) and ORR (0% vs. 35.0% vs. 43.8%) of patients with gBRCA mutation was inferior to patients with gBRCA wt and patients with unknown gBRCA status. And simultaneously, the DCR of patients with gBRCA mutation was worse than patients with gBRCA wt (33.3% vs. 75.0%, P=0.039) and patients with unknown gBRCA status (33.3% vs. 81.3%, P=0.032). No statistically significant differences were found in OS. Our study findings indicating that germline BRCA mutation may affect the clinical outcomes of metastatic breast cancer treated with CDK4/6 inhibitor. Additionally, the results support incorporating gBRCA mutation into systemic therapy decisions for patients with HR+/HER-2- metastatic breast cancer treated with CDK4/6 inhibitor.