Real-World Analysis of Breast Cancer Patients Qualifying for Adjuvant CDK4/6 Inhibitors

Area of Science:

• Oncology
• Clinical Trials
• Pharmacology

Background:

• Adjuvant CDK4/6 inhibitors (abemaciclib, ribociclib) have demonstrated improved disease-free survival (DFS) in hormone receptor-positive, HER2-negative early breast cancer (EBC).
• The monarchE and NATALEE trials established the efficacy of these agents in specific EBC populations.

Purpose of the Study:

• To assess the real-world proportion of EBC patients eligible for adjuvant CDK4/6 inhibitors.
• To evaluate the outcomes of these eligible patients in a real-world setting.

Main Methods:

• Analysis of consecutive female patients with HR-positive, HER2-negative EBC (1997-2017) from a regional registry.
• Eligibility criteria for abemaciclib and ribociclib based on nodal status, tumor size, and grade were applied.

Main Results:

• 17.5% of patients were eligible for abemaciclib and 41.3% for ribociclib.
• 5-year DFS was 77% for eligible abemaciclib patients vs. 94% for non-eligible (HR 2.6).
• 5-year DFS was 86% for eligible ribociclib patients vs. 97% for non-eligible (HR 1.92).
• Real-world eligible patients were older and had lower nodal burden compared to trial cohorts.

Conclusions:

• A significant proportion of EBC patients meet eligibility criteria for adjuvant CDK4/6 inhibitors, presenting resource and workforce considerations.
• Real-world eligible patients often have less advanced disease than trial participants, suggesting a potentially smaller absolute treatment benefit.