Background <p>Folate receptor alpha (FRα, FOLR1) is the required biomarker for mirvetuximab soravtansine, a treatment option for patients with platinum-resistant ovarian cancer. Since its approval, the drug has been introduced into national drug programs, but prevalence data from the Polish population are lacking. This study provides the first multicenter assessment of FOLR1 expression in Polish ovarian cancer in the context of treatment eligibility.</p> Methods <p>We retrospectively analyzed two institutional cohorts comprising 229 epithelial ovarian cancer cases from the Oncology Center in Bydgoszcz and the National Institute of Oncology in Warsaw. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded tissue using the VENTANA FOLR1 (FOLR1-2.1) RxDx Assay on the BenchMark ULTRA platform. Membranous staining of moderate or strong intensity in ≥ 75% of viable tumor cells was considered positive, in accordance with criteria for FOLR1-targeted therapy.</p> Results <p>Positive FOLR1 expression was observed in 116 of 229 (50.7%, 95% CI 44.2–57.2) analyzed tumors, with 40% showing high expression. In most of these cases, staining intensity was moderate to strong, meeting the established threshold for therapeutic eligibility. In ~ 18% of tumors, FOLR1 expression fell into the borderline range (65–85%).</p> Conclusion <p>Approximately half of the ovarian cancer patients in this multicenter Polish cohort demonstrated FOLR1 positivity. Although this prevalence is lower than that reported in high-grade serous carcinoma cohorts, it likely reflects histological heterogeneity and methodological differences between studies. These findings provide the first population-based evidence from Poland and support the implementation of FOLR1 testing to guide access to mirvetuximab soravtansine. Further research integrating clinical and molecular data is warranted to validate these results and assess implications for cost-effectiveness and patient outcomes.</p>