Evaluation of Laboratory-Derived Immunohistochemical Assays for Folate Receptor α Expression in Epithelial Ovarian Cancer and Comparison With a Companion Diagnostic.

Context.—: The VENTANA FOLR1 (FOLR1-2.1) RxDx (FOLR1 CDx) assay, developed by Roche Tissue Diagnostics, is a Food and Drug Administration-approved immunohistochemical assay intended for use in the assessment of folate receptor α (FRα) expression in formalin-fixed, paraffin-embedded epithelial ovarian, fallopian tube, and primary peritoneal tumor specimens. No published reports have compared the performance of other available FRα antibodies with the approved FOLR1 CDx.

Objective.—: To assess the performance of research FRα laboratory-developed tests compared with the FOLR1 CDx.

Design.—: The performance of 6 FRα-targeting antibodies was compared with the approved FOLR1 CDx in normal fallopian tube specimens. Two antibodies were selected for further assessment and compared with the FOLR1 CDx in ovarian tumor specimens.

Results.—: Of the 6 antibodies tested, 4 displayed a lack of specific membrane staining and/or high background, whereas 2 antibodies, produced by Leica Biosystems and Biocare Medical, respectively, exhibited specific and sensitive FRα staining. When assessed for their ability to correctly identify FRα-positive samples (per the FOLR1 CDx label, ≥75% of viable tumor cells with moderate and/or strong membranous staining intensity), both assays overpredicted FRα positivity compared with the FOLR1 CDx in archival ovarian tumor samples.

Conclusions.—: These data highlight the need for caution in antibody selection when developing immunohistochemistry-based assays, as some antibodies failed to cleanly and specifically identify FRα expression. We identified 2 antibodies appropriate for further investigation; however, as developed, these antibodies may overselect patients for treatment with FRα-targeted therapies.