Statistical analyses
Quantitative variables were analysed and presented as mean (standard deviation [SD]) or median (interquartile range [IQR]; or range [minimum–maximum]), as appropriate. Categorical variables were presented as absolute and relative (%) frequency for each class. Denominators are presented where analyses were conducted in a subset of patients. Time-to-event outcomes (PFS, OS and treatment duration) were analysed and presented using the Kaplan–Meier method, with results reported as median (95% confidence intervals [CI]) and/or 12- and 24-month rates. Patients who were event-free were censored on the last date they were known to be event-free for the outcome of interest. Regarding missing data, standard imputation was used for missing dates (missing days were assumed to be the 15th of the month; missing days and month were assumed to be the 1st of July) and menopausal status (patients over the age of 60 years were assumed to be post-menopausal, 45–60 years were recorded as unknown and under 45 years were assumed to be pre-menopausal). No other imputation of missing data was conducted, and the number of patients with missing data was reported; patients with missing data were included in the calculation of percentages. All endpoints were analysed in the overall population. Subgroup analyses were conducted to describe clinical outcomes in the following subgroups: palbociclib treatment line; patients with de novo and non-de novo (relapsed) MBC; and patients with early (≤12 months) and late (>12 months) relapse (disease-free interval). The database was locked on the 4th of April 2021, and data were analysed using R studio version 3.6.1 and R studio version 1.2.1335.