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BACKGROUND This pooled analysis of MONALEESA trials evaluated the safety of ribociclib plus endocrine therapy (RIB + ET) with a focus on dose reductions in first-line patients. METHODS In the dose reduction analysis, data were pooled from MONALEESA-2 (all patients), MONALEESA-3 (patients receiving treatment as first-line ET) and MONALEESA-7 (patients receiving combination therapy with an NSAI as initial ET). Efficacy was analysed by ribociclib relative dose intensity (DI). Safety was analysed in all patients in the trials (except those receiving tamoxifen in MONALEESA-7) and those with/without ≥1 ribociclib dose reduction. RESULTS Of 818 women who received first-line RIB + ET, 41.8% required ≥1 dose reduction due to AEs (most commonly, neutropenia). Median RIB relative DI in patients without and with dose reductions was 99.3% and 65.6% in MONALEESA-2, 98.4% and 67.8% in MONALEESA-3 and 98·0% and 66·3% in MONALEESA-7. Median PFS was 24.8, 24.9 and 29.6 months for patients who received ≤71% (30th percentile), 72-96% (60th percentile) and 97-100% (90th percentile) RIB relative DI, respectively. No new safety signals emerged in the pooled safety analysis. CONCLUSIONS This analysis provides reassuring data showing that the clinical benefit of RIB is preserved when dose modifications are undertaken to manage AEs. TRIAL REGISTRATION MONALEESA-2 (NCT01958021) first posted October 8, 2013; MONALEESA-3 (NCT02422615) first posted April 21, 2015; MONALEESA-7 (NCT02278120) first posted October 29, 2014.