ESR1 Mutations in Metastatic Hormone Receptor-Positive Breast Cancer in the Greek Population

The goal of this observational study is to assess the prevalence of ESR1 mutations in patients with metastatic hormone receptor-positive/HER2-negative breast cancer in Greece and evaluate the associations of these mutations with disease characteristics, clinical outcomes and real-world treatment patterns. This study will include participants who have already undergone ESR1 testing as part of their standard medical care. Patient real-world data will be extracted by the patient's medical records. No additional procedures or visits beyond routine care will be required. Data will be collected from routine clinical visits and standard-of-care treatment.