Eligibility for adjuvant CDK4/6 inhibitors in HR+/HER2− early breast cancer: insights from a large cohort in central south China

Background: The MonarchE and NATALEE trials have established adjuvant CDK4/6 inhibitors (abemaciclib and ribociclib) as pivotal therapies for high-risk hormone receptor-positive (HR+) early breast cancer (EBC). However, real-world data regarding the populations eligible for these trials remains limited, especially in Asian cohorts, highlighting the need for data that bridges the gap between trial findings and clinical practice in diverse settings. We conducted this real-world study in a central Chinese population to identify patient characteristics potentially associated with clinical benefits from CDK4/6 inhibitors such as abemaciclib and ribociclib. Methods: This retrospective study analyzed 1,947 patients with stage I-III HR+ invasive breast cancer (BC) treated at Xiangya Hospital, China, from 2015 to 2021. The clinicopathological profiles of patients meeting the eligibility criteria of the MonarchE and NATALEE trials were compared. Eligibility was defined according to trial-specific inclusion criteria: MonarchE required ≥4 positive lymph nodes (LNs) or 1-3 LNs with tumor size ≥5 cm or grade 3 histology (Cohort 1), or 1-3 LNs with Ki-67 ≥20% (Cohort 2). NATALEE included stage IIB-III and high-risk stage IIA (T2N0 with grade 3 or Ki-67 ≥20%). Results: 49 years) and showed greater heterogeneity in Ki-67 expression (44.9% had Ki-67