Characteristics of Patients With Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Early Breast Cancer Eligible for Adjuvant Cyclin-Dependent Kinase 4/6 (CDK4/6) Inhibitors: Real-Life Evidence in a Colombian Cancer Center.

Background The introduction of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in the adjuvant setting for hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) early breast cancer (BC) has expanded treatment options for high-risk patients. However, real-world data on eligibility for these therapies in Latin American populations remain limited. Methods This retrospective study analyzed 334 patients with HR+/HER2- early breast cancer (stages I-III) treated at a Colombian cancer center (2022-2024). Eligibility criteria for adjuvant abemaciclib (monarchE) and ribociclib (NATALEE) trials were applied. Clinicopathological characteristics and treatment patterns were assessed. Results Among abemaciclib-eligible patients (36.2%, n=121), 54.5% had ≥4 positive nodes, and 45.5% met alternative high-risk criteria (1-3 nodes plus tumor size of ≥5 cm or grade 3 or Ki-67 of ≥20%). Ribociclib-eligible patients (59%, n=197) included 53.8% with stage III disease and 12.7% with node-negative, grade 3 tumors. Descriptive comparison with pivotal trials shows that compared to pivotal trials, our cohort had an older median age (61 versus 51-52 years) and a lower prevalence of grade 3 tumors (17.1% versus 30%-40%). Conclusion A substantial proportion of Colombian patients with HR+/HER2- early breast cancer qualify for adjuvant CDK4/6i, particularly those with nodal involvement. These findings highlight both the clinical opportunity and economic challenges of implementing these therapies in resource-limited settings while underscoring the need for improved early detection to reduce advanced presentations. Eligibility based on clinical-pathological criteria identifies a high-risk group, though optimal selection may require biomarker refinement where available.