This is a retrospective cohort study utilizing the US Optum research administrative claims database. Adult female patients who had HR+/HER2- mBC were identified and included in the study. These patients were stratified into three cohorts based on the first CDK4/6i received (ribociclib, palbociclib, or abemaciclib).
* Study period: Period during which all relevant medical and pharmacy information in the database was retrieved
* Index event identification period: time frame during which index treatment was identified
* First CDK4/6i: the date on which patients initiated their first treatment after being diagnosed with HR+/HER2- mBC; this date was considered as the index date
* Baseline period: Time frame during which patient characteristics, prior mBC treatments, and concomitant treatments received by CDK4/6i-naïve patients were evaluated
* Follow-up period: time frame on and after the index date during which patients' treatments and dosing patterns were observed
Establishment of baseline period Health plan enrollment in the three months prior to the index treatment was included in the baseline period. Patient demographics, clinical characteristics, National Cancer Institute (NCI) comorbidity index, concomitant medication use that can potentially lead to a DDI, and other BC treatments prior to the index treatment were evaluated during this period.
Establishment of follow-up period Patients were observed for ≥3 months starting from the index date until the end of the study period or continuous enrollment or until the time when patients switched to another therapy (including another CDK4/6i), whichever came first. Dosing patterns for CDK4/6i were evaluated in the follow-up period. Analyses were conducted at key time points of 3, 6, and 12 months
