Simple Summary
Reliable testing of folate receptor alpha is essential to identify patients who may benefit from a targeted treatment for ovarian cancer. In Europe, laboratories currently may use different antibodies and staining systems, but it is not known whether these approaches provide comparable results. In this study, we conducted a large quality assessment to examine how well different laboratories and methods can detect folate receptor alpha in ovarian cancer samples. We found that the currently approved test (companion diagnostics by Roche VENTANA) showed the most consistent performance, while several widely used alternative antibodies often produced weak staining or false positive results. Our work highlights the importance of conducting open proficiency trials to evaluate alternative biomarker testing approaches.


Abstract
Background: Folate receptor alpha (FRα) is a glycosylphosphatidylinositol-anchored membrane protein encoded by the FOLR1 gene. Its overexpression in various cancers, including ovarian carcinoma, makes it a promising target for antibody-drug conjugates (ADC). Mirvetuximab soravtansine-gynx, an FRα-targeting ADC, has been approved by the FDA and EMA for the treatment of FRα-positive, platinum-resistant ovarian cancer. In the United States, patient selection is tied to the VENTANA FOLR1 (FOLR1-2.1) RxDx Assay, an immunohistochemical (IHC) test that identifies tumors with ≥75% moderate-to-strong membrane staining. However, in the European Union, no specific IHC test is mandated, and alternative antibodies are frequently used in routine pathology, necessitating validation of their diagnostic performance. Methods and Results: We report the results of the first interlaboratory proficiency trial on FRα testing conducted by the German Quality Assurance Initiative in Pathology (QuIP®). Sixty-eight pathology institutes participated across internal and open trials using a variety of antibodies and staining platforms. The VENTANA FOLR1 RxDx Assay demonstrated the highest reliability, with 83% of participating laboratories achieving a successful result. In contrast, alternative clones such as BN3.2 (Leica/Novocastra) and EPR20277 (Abcam) showed substantially weaker staining intensity, lower concordance with reference values, and success rates of only 22–25%, while other antibodies failed entirely. Problem analysis revealed that failures with the VENTANA FOLR1 (FOLR1-2.1) RxDx Assay were mainly due to interpretative challenges, whereas weak staining was the predominant issue with alternative clones. Participation in a preparatory online seminar improved pass rates, underscoring the importance of training. Conclusions: These findings highlight the critical importance of standardized, validated assays for FRα detection to ensure accurate patient selection for targeted therapies. The study emphasizes the need for further optimization of alternative antibodies before clinical implementation.