Study design and participants
PD, cardiac dysfunction, SD
DISEASE, BEST
The MONALEESASIA (NCT02333370) study design was previously published [Both Japanese and non-Japanese patients underwent dose-escalation and dose-expansion phases. In the dose-escalation phase, non-Japanese patients received ribociclib (400 mg or 600 mg on a 3-weeks-on/1-week-off schedule) plus letrozole (2.5 mg daily), and Japanese patients received ribociclib (300 mg or 400 mg on a 3-weeks-on/1-week-off schedule) plus letrozole (2.5 mg daily). In the dose-expansion phase, non-Japanese patients received ribociclib (600 mg on a 3-weeks-on/1-week-off schedule) plus letrozole (2.5 mg daily). Dose reduction of ribociclib to a minimum of 200 mg was allowed in both groups [Key exclusion criteria included prior CDK4/6i use, major surgery ≤ 14 days prior to start of study treatment, and a history of cardiac dysfunction or disease. No prior ET or chemotherapy in the advanced setting was permitted, except for in Japanese patients, for whom 1 prior ET for ABC was permitted in the group receiving ribociclib plus fulvestrant.The primary end points were the maximum tolerated dose and/or recommended Phase 2 dose in the dose-escalation phase and the safety and tolerability of ribociclib plus ET in the dose-expansion phase [Best overall response (BOR) of individual patients was classified as complete response (CR), partial response (PR), stable disease (SD), or progressive disease (PD) according to RECIST 1.1.