An observational study in ESR1 Gene Mutation, Breast Cancer (Locally Advanced or Metastatic) and Hormon Receptor Positive Breast Cancer, sponsored by Hellenic Cooperative Oncology Group. Recruiting at 1 site in Greece. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-27.
Sponsored by Hellenic Cooperative Oncology Group · Observational
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.
This is a non-interventional, retrospective and prospective observational study conducted in routine clinical practice in Greece with the support of the Hellenic Cooperative Oncology Group. The study involves the collection of primary data from oncology centers, including a representative sample of patients receiving standard-of-care treatment. No changes to current therapeutic practice are required, and all patient management will follow local clinical standards under the discretion of participating physicians.
Eligible participants are patients aged 18 years or older, with histologically confirmed metastatic hormone receptor-positive, HER2-negative breast cancer who undergo ESR1 mutation testing.
The primary endpoint of the study is the epidemiology of ESR1 mutations in the Greek population of patients with metastatic hormone receptor-positive breast cancer, while secondary endpoints include the association of ESR1 mutations with the number and type of prior therapies and correlation with other biomarkers.
Clinical data will be extracted from patients' medical records. Personal identifiers will be pseudonymized, coded, and assigned a unique identification number to protect patient privacy. For the retrospective portion of the study, approval will be obtained from the hospital Scientific Board for patients who are no longer alive, under a waiver of consent.
Patients who consent to participate in optional translational research may provide biological material for further study. This may include paraffin-embedded tumor tissue blocks, surgical specimens, H\&E slides for molecular tumor characterization or digitization for deep learning-based biomarker prediction, and swab samples for germline mutation analysis, provided the patient is alive.
The study will be conducted in accordance with Good Pharmacovigilance Practice, the European General Data Protection Regulation (GDPR), and applicable local regulatory requirements.
12,828 studies on the registry are indexed under Breast Neoplasms; 2,923 are open to participants now.
This study's planned enrollment of 500 is above the median of 185 across 2,712 observational studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Hellenic Cooperative Oncology Group is the lead sponsor of 61 studies on the registry; 5 are open to participants now.
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The study population includes patients with metastatic hormone receptor-positive (HR+) breast cancer in Greece who have been tested for ESR1 mutations. Patients are enrolled from routine clinical practice, including both retrospective and prospective data collection. All treatments follow standard clinical practice, and no additional interventions or study-specific procedures are required. Data collected include ESR1 mutation status (via NGS liquid biopsy), clinicopathological characteristics, and treatment patterns
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Patients with histologically confirmed metastatic breast cancer with positive hormone receptors and negative HER2 status.
Patients undergoing ESR1 mutation testing.
Exclusion Criteria:
Patients with metastatic HR-positive/HER2-negative breast cancer in Greece who have been tested for ESR1 mutations. Data collected include ESR1 mutation status (via NGS liquid biopsy), clinicopathological features, and treatment patterns in routine clinical practice. No changes to standard therapy are required, and data collection occurs only during routine clinical visits
Prevalence of ESR1 mutations
The proportion of patients with metastatic HR+/HER2- breast cancer in Greece who have detectable ESR1 mutations, determined by next-generation sequencing (NGS) of circulating tumor DNA (liquid biopsy) among all patients tested. Data are collected retrospectively and prospectively from routine clinical visits.
Time frame: through study completion, an average of 1 year
Association of ESR1 mutations with clinicopathological features
Correlation of ESR1 mutation status with patient demographics, tumor subtype, prior therapies, disease progression, and other clinicopathological characteristics observed in routine clinical practice.
Time frame: through study completion, an average of 1 year
Plan to share: No
Started May 2025 (actual). Primary completion is estimated for May 2027, 24 months after the start.
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From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Hellenic Cooperative Oncology Group