Abstract PS1-12-25: Institutional adherence to CDK4/6 inhibitor use in ER+/HER2- metastatic breast cancer: A retrospective cohort study

Abstract Background: NCCN recommends the combination of CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) as the standard first line treatment in ER+/HER2- metastatic breast cancer (MBC). Despite CDK4/6i demonstrating significant progression-free survival in clinical trials, real-world adherence to this combination remains inconsistent. We characterize the factors that influenced the adherence to combination therapy in patients with ER+/HER2- MBC. Methods: We conducted a multi-center retrospective review of electronic health records of patients with ER+/HER2- MBC between years 2015 - 2022 and imputed data into a standardized REDCap database. Bivariate group comparisons were performed using chi-squared or ANOVA, as appropriate. Multivariate logistic regression was done to identify independent factors associated with adherence to combination therapy. Statistical analyses were performed using R. A p-value