In recent years, cyclin-dependent kinase 4 & 6 (CDK4/6) inhibitors have transformed the treatment landscape of patients with metastatic HR+/HER2- BC. Inspired by the successes in the advanced setting, CDK4/6 inhibitors are now also being evaluated in earlier disease stages. The phase III MonarchE trial investigates the combination of abemaciclib with ET as adjuvant therapy for resected, high-risk, node-positive, HR+/HER2- early BC (N=5,637).
Previously, an interim analysis of this study demonstrated a statistically significant improvement in iDFS for patients treated with abemaciclib + ET compared to ET alone. At SABCS 2020, the final primary outcome analysis was presented with a median follow-up of 19 months. In this final analysis, abemaciclib plus ET continued to demonstrate a superior iDFS, compared to ET alone with two-year iDFS rates of 92.3% and 89.3%, respectively (HR[95%-CI]: 0.713[0.583–0.871], p=0.0009). This corresponds to a 28.7% reduction in the risk of developing invasive disease for patients treated with the CDK4/6 inhibitor.
This iDFS benefit in favour of abemaciclib was observed across all subgroups and similar results were obtained in terms of distant recurrence free survival (DRFS) (HR[95%CI]: 0.609[0.445–0.833], p=0.0018). In patients with centrally assessed high Ki-67 (>20% Ki-67), a two-year iDFS rate of 91.6% and 87.1% was observed for patients treated with abemaciclib plus ET vs. ET alone (HR[95%CI]: 0.691[0.519–0.920], p=0.0111). As such, these findings indicate that abemaciclib is also effective in high-tumour burden settings.
Feys T, Rawson T. Highlights in Luminal Breast Cancer. San Antonio Breast Cancer Symposium Special. 2020 December:10-18.