Ethnicity-based comparative analysis of adverse effects in 30,000 HR+/HER2- metastatic breast cancer patients treated with CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib): A real-world meta-analysis

Abstract

Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) with endocrine therapy are standard of care for hormone receptor-positive, HER2-negative metastatic breast cancer (HR+/HER2- MBC), although drug-specific adverse effect (AE) profiles vary. As clinical trials have limited ethnic representation, this meta-analysis uses real-world evidence to assess AEs associated with palbociclib, abemaciclib, and ribociclib across ethnic groups. Method(s): Following PRISMA guidelines, MEDLINE and Embase were searched; 116 studies were included (Palbociclib: 67, Abemaciclib: 29, Ribociclib: 20). All estimates are reported with 95% confidence intervals (CI) unless specified otherwise. Result(s): Palbociclib 23786 patients (Asian (AS): 18124; White (WH): 4581; Black (BL): 347; Mixed Ethnicity (MX): 734; mean age: 57y) were included. Frequently reported AEs were neutropenia (67%), leukopenia (61%), and anaemia (31.5%). AS patients exhibited the highest incidence of neutropenia (72.0%) and leukopenia (76.7%), while BL and MX patients showed highest incidences of Anemia (33.8%). Meta-regression showed ethnicity was not a significant moderator of AE risk (p > 0.05). Abemaciclib Among 4,715 patients (AS: 2,429; WH: 2,223; BL: 32; MX: 21; mean age: 62.4 years), considerable ethnic variation was observed in Grade >=3 neutropenia. Incidence was higher in AS patients (52.8%) compared to WH (16%) and BL (12%). AS patients had the highest rates of leukopenia (77.4%) and anaemia (33.7%), while WH patients exhibit the lowest incidence across AEs. Ribociclib An analysis of 4,157 patients (WH: 2,189; AS: 1,514; BL: 131; MX: 323; mean age: 59.8 years) showed the highest incidence of Grade >=3 neutropenia (45.8%; p < 0.0001), leukopenia, and anaemia in AS patients. WH patients had lower rates of haematological toxicity, while BL and MX cohorts showed intermediate incidence patterns. Conclusion(s): This meta-analysis identifies drastic ethnic disparities in haematological toxicity, particularly in AS. Results highlight the need for diverse RCT recruitment and standardised AE reporting to optimise personalised treatment. Legal entity responsible for the study: Olivia Benny. Funding(s): Has not received any funding. Disclosure: All authors have declared no conflicts of interest. Copyright © 2026