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

• Published in: Clinical breast cancer
• Main Authors: Kanjanapan, Yada, Anderson, Wayne, Smith, Mirka, Green, Jenny, Chalker, Elizabeth, Craft, Paul
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 29.08.2024
• Subjects: Abemaciclib; Adjuvant therapy; Breast cancer; CDK4/6 inhibitors; Ribociclib; Ribociclib; Abemaciclib; Breast cancer; Adjuvant therapy; CDK4/6 inhibitors
• ISSN: 1526-8209; 1938-0666; 1938-0666
• DOI: 10.1016/j.clbc.2024.08.022

Adjuvant CDK4/6 inhibitors abemaciclib and ribociclib improved disease-free survival (DFS) added to endocrine therapy in hormone receptor (HR)-positive HER2-negative early breast cancer (EBC), in monarchE (NCT03155997) and NATALEE (NCT03701334) trials respectively. We assessed the proportion and outcome of EBC patients qualifying for adjuvant CDK4/6 inhibitors in the real-world. Consecutive female patients with HR-positive HER2-negative EBC between 1997 and 2017 from the Australian Capital Territory and South-East New South Wales Breast Cancer Treatment Group registry were analyzed. Patients eligible for abemaciclib had ≥4 axillary nodes involved or 1-3 nodes plus primary >5 cm or grade 3. Ribociclib eligibility was defined as node-positive and node-negative with primary >5 cm or >2 cm grade 3. Of 3840 patients, 671 (17.5%) were abemaciclib-eligible and 1587 (41.3%) ribociclib-eligible . The 5-year DFS was 77% and 94% in abemaciclib-eligible and noneligible registry patients respectively (HR 2.6, 95% CI 2.26-3.05, P < .001). The 5-year DFS was 86% and 97% in ribociclib-eligible and noneligible registry patients respectively (HR 1.92, 95% CI 1.67-2.19, P < .001). Compared with monarchE trial patients, abemaciclib-eligible registry patients were older (median 55 years in registry vs. 51 years in trial), with lower nodal burden (≥4 nodes in 44% in registry vs. 60% in trial). There were more stage III cancers in NATALEE trial patients (60%) than ribociclib-eligible registry patients (24%). Many women with EBC will qualify for adjuvant CDK4/6 inhibitors (17.5% abemaciclib, 41.3% ribociclib) with resource and workforce implications. In the real-world setting, a greater proportion of adjuvant CDK4/6-eligible patients have lower stage disease, therefore the absolute benefit from treatment may be smaller than estimated by the trials. Adjuvant CDK4/6 inhibitors improved disease-free survival in high-risk hormone receptor-positive HER2-negative breast cancer in phase III trials. Our retrospective analysis of 3840 women from an Australian real-world registry found 17.5% meet abemaciclib and 41.3% meet ribociclib-eligiblity. Phase III study population have higher risk (stage and nodal burden) and may overestimate the benefit from adjuvant CDK4/6 inhibitors in the real-world setting.