# Folate receptor alpha expression (FRα-positive, PS2+ >= 75%)

Source: https://onco.cc/biomarkers/folr1-expression/  
OnCo record `folr1-expression` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Folate receptor alpha is a surface protein on most high-grade serous ovarian cancers. Mirvetuximab soravtansine requires FRα-positive disease, scored as at least 75 percent of cells with moderate or strong staining on the Ventana FOLR1 assay.

## Summary

Mirvetuximab soravtansine (Elahere) is labelled for FRα-positive platinum-resistant epithelial ovarian, fallopian tube or primary peritoneal cancer after one to three prior regimens, selected with an FDA-approved test; the VENTANA FOLR1 (FOLR-2.1) RxDx Assay scores positive at 75 percent or more of viable tumour cells with moderate (2+) or strong (3+) membrane staining (PS2+ >= 75 percent), the SORAYA and MIRASOL definition. About 35 to 40 percent of high-grade serous cancers are FRα-high by this rule.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: FRα; FRa; folate receptor alpha positive; FOLR1 expression; FRα-positive; PS2+ >= 75%; FOLR1 IHC
- Tags: biomarker; surface-antigen

## Sources

- ELAHERE prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=00c424b5-6ccd-48ab-9e88-1986451120e2

## Connected records

- biomarkers: [HRD-positive (genomic instability score)](https://onco.cc/biomarkers/hrd-positive/), [Tissue factor expression](https://onco.cc/biomarkers/tissue-factor-expression/), [Tumour (somatic or germline) BRCA1/2 mutation and HRR gene alterations](https://onco.cc/biomarkers/brca-somatic/)
- cancers: [Endometrial cancer](https://onco.cc/cancers/endometrial/), [High-grade serous ovarian cancer](https://onco.cc/cancers/high-grade-serous-ovarian-cancer/), [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Platinum-resistant ovarian cancer](https://onco.cc/cancers/platinum-resistant-ovarian-cancer/)
- drugs: [Mirvetuximab soravtansine](https://onco.cc/drugs/mirvetuximab-soravtansine/)
- terms: [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [Platinum-sensitive / platinum-resistant](https://onco.cc/terms/platinum-sensitivity/)
- targets: [Folate receptor alpha](https://onco.cc/targets/folr1/)

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