Folate Receptor Alpha (FRα) Expression and Heterogeneity in Epithelial Ovarian Cancer

This is a single-country, retrospective, observational biomarker study conducted in Greece to evaluate Folate Receptor Alpha (FRα) expression in patients with high-grade serous ovarian, fallopian tube, and primary peritoneal cancer at the time of diagnosis. Approximately 200 eligible female patients (≥18 years) diagnosed between 1 January 2001 and 30 July 2025 will be included from around 15 clinical sites affiliated with the Hellenic Cooperative Oncology Group. Historically collected Formalin-Fixed Paraffin-Embedded (FFPE) tissue samples stored in the Hellenic Cooperative Oncology Group biobank will be analyzed centrally using the Ventana FOLR1 RxDx assay to determine FRα expression. Only samples collected at initial diagnosis will be included; relapse samples will be excluded. The primary objective is to assess the prevalence of FRα-positive status, defined as ≥75% viable tumor cells with moderate (2+) and/or strong (3+) membrane staining. Secondary objectives include evaluation of intra-tumoral heterogeneity, concordance between primary and metastatic lesions, prevalence of lower FRα expression levels, and associations between FRα expression and clinical characteristics, BRCA/HRD status, progression-free survival (PFS), and overall survival (OS). All analyses will be descriptive, with additional exploratory statistical methods including chi-square tests, Cohen's kappa, correlation analyses, ANOVA, Kaplan-Meier survival analysis, and Cox proportional hazards models. Data will be retrospectively collected from the Hellenic Cooperative Oncology Group registry and medical records and entered into a secure REDCap eCRF system.

Inclusion Criteria: * Female patients. * 18 years of age or older. * Patients diagnosed with high-grade serous epithelial ovarian cancer according to pathologists' report. Exclusion Criteria: * Diagnosis of non-epithelial ovarian tumors * Diagnosis of endometrioid, mucinous, or clear cell carcinomas. * Inadequate (poor quality or inadequate posology for analysis) tissue samples.