BACKGROUND: Palbociclib is currently the most commonly used cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) for patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) in Europe since its approval in 2017. However, large-scale assessments of palbociclib utilization and subsequent clinical outcomes in real-world settings are limited. Documentation of longitudinal treatment patterns and effectiveness following initiation of first-line (1L) palbociclib + aromatase inhibitor (AI) in more heterogeneous, real-world patient populations are needed to complement clinical trial findings. STATISTICAL METHODS: All study measures will be summarized descriptively. Time-to-event outcomes will be estimated using the Kaplan-Meier method. Direct covariate matching at the site-level and inverse probability weighting using propensity scores is planned to account for differences in baseline patient and clinical characteristics between treatment groups in the exploratory comparative analysis.
TRIAL DESIGN: This is an observational cohort study using retrospective data abstracted from the medical records of patients with HR+/HER2- ABC who initiated 1L treatment (index date) with palbociclib + AI (September 2016-July 2020) or AI monotherapy (January 2010 to July 2020) as 1L therapy for ABC. Patients' study index dates will be at least 12 months before the data abstraction date to allow a minimum potential follow-up of at least 12 months. Patients who died within < 12 months after the index date will remain eligible.
ELIGIBILITY CRITERIA: Adult patients who received a de novo or a recurrent diagnosis of locally advanced BC (i.e., not amenable to curative therapy) or metastatic BC will be included. Patients who participated in a clinical trial for ABC, had evidence of prior other malignant neoplasm, received any CDK4/6i for early stage disease, and received other CDK4/6i for ABC will be excluded.
STUDY AIMS: This study aims to describe patient characteristics, treatment patterns, and clinical outcomes among patients with HR+/HER2- ABC in Europe who received 1L CDK4/6i treatment. Key outcomes of interest include real-world tumor response, real-world progression-free survival, and overall survival. An exploratory objective will be to compare clinical outcomes between patients treated with 1L palbociclib + AI versus AI monotherapy.
TARGET ACCURAL: Data abstraction is anticipated to begin in September 2021. Data will be abstracted for up to 2,400 eligible patients. Approximately 60 total sites from across Germany, Spain, and the United Kingdom and, if feasible, from other European countries will be recruited.
