Matching-adjusted indirect comparison of ribociclib + nonsteroidal aromatase inhibitor versus abemaciclib + endocrine therapy in hormone receptor-positive/HER2-negative early breast cancer

<b>Aim:</b> Ribociclib + nonsteroidal aromatase inhibitor (NSAI) and abemaciclib + endocrine therapy (ET) are approved for high-risk hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) early breast cancer based on data from the NATALEE and monarchE trials, respectively. No trials have directly compared efficacy and safety of adjuvant ribociclib and abemaciclib. This study compared relative efficacy and safety of adjuvant ribociclib + NSAI versus abemaciclib + ET using matching-adjusted indirect comparison (MAIC). <b>Materials & methods:</b> Individual patient data from NATALEE and aggregate data from monarchE were analyzed, with patients from NATALEE selected to match the key eligibility criteria of monarchE cohort 1. Unanchored MAIC was used to compare invasive disease-free survival, distant relapse-free survival, and grade ≥3 treatment-emergent adverse events between treatment arms in NATALEE versus monarchE. Cox regression was used to estimate hazard ratios pre- and post-MAIC weighting. Logistic regression was used to estimate odds ratios (ORs). <b>Results:</b> After weighting, the effective sample size for the ribociclib + NSAI arm of NATALEE was 448. Cox regression yielded similar invasive disease-free survival with weighted ribociclib + NSAI versus abemaciclib + ET (hazard ratio, 0.901; 95% CI: 0.678-1.197). Unweighted efficacy comparisons were consistent with the weighted approach. Lower odds (OR <1) for diarrhea, leukopenia and lymphopenia and higher odds (OR >1) for increased alanine aminotransferase and neutropenia with ribociclib + NSAI versus abemaciclib + ET were noted before and after weighting. Sensitivity analyses were consistent with the primary analysis. <b>Conclusion:</b> This MAIC suggests similar efficacy between ribociclib + NSAI and abemaciclib + ET but different safety profiles in the HR+/HER2- early breast cancer patient population corresponding to the monarchE cohort 1, which has implications for treatment decisions. This analysis has limitations inherent to unanchored MAIC and should be interpreted in context of the trials and with clinical judgement.