Comparative real-world survival outcomes of ribociclib and abemaciclib in breast cancer.

11167 Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), including ribociclib and abemaciclib, are widely used in hormone receptor–positive, HER2-negative high-risk early-stage breast cancer in combination with endocrine therapy. While randomized trials have demonstrated survival benefits, comparative real-world outcomes between these agents remain limited. This study evaluates all-cause mortality among patients treated with ribociclib versus abemaciclib using a large real-world database. Methods: We conducted a retrospective cohort study using the TriNetX US Collaborative Network, a global federated health research network, including adult patients with breast cancer treated with ribociclib (n = 7,697) or abemaciclib (n = 12,626) within the past 20 years. Two cohorts were constructed and balanced using 1:1 propensity score matching (PSM) based on age at diagnosis, sex, and race. The primary outcome was all-cause mortality at 1, 3, and 5 years. Kaplan–Meier survival curves and Cox proportional hazards models were used to estimate survival probabilities and hazard ratios. Results: After PSM, a total of 15,374 patients were included (7,687 per cohort). Mean age was 60.2±13.5 years in the ribociclib cohort and 60.2±13.4 years in the abemaciclib cohort. Most patients were female (99%) and White (72%). At 1 year, survival probability for ribociclib was 91.5% compared with 89.0% for abemaciclib (hazard ratio 0.74, 95% CI 0.66–0.84; log-rank p < 0.001). There was no significant difference in survival probabilities at 3 years (70.1% vs 72.1%) or 5 years (56.6% vs 55.1%), with hazard ratios not significantly different from 1.0. Conclusions: In this real-world analysis, ribociclib use was associated with lower all-cause mortality at 1 year compared with abemaciclib; however, this difference did not persist at longer follow-up. These findings should be interpreted cautiously given potential residual confounding and differences in clinical indications between agents. Further studies accounting for disease stage and treatment context are warranted.