Estimation of the Prevalence of HER2 Low and Describe the SoC, Treatment Patterns, and Outcome in Real-world Practice Among Unresectable and/or Metastatic Breast Cancer Patients With HER2 Low Status

The data source for this project will be HER2 IHC historical scores, local lab rescoring of historical HER2 fixed tissue slides, independent central retesting or local lab retesting (under special occasions) of HER2 IHC status for enrolled patients who have available tissue, other biomarker testing results based on historical testing and/or testing of archived tissue samples when available, and curated patient-level data. Real-world data sources include electronic health records/electronic medical records (EHR/EMR) and biobank registries. Data from EHR/EMR sources will be curated. Biobank tissue for enrolled patients who have multiple samples available will be selected consecutively when possible and will start with the latest available samples then move backward in time.