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

aka FRα, FRa, folate receptor alpha positive, FOLR1 expression, FRα-positive, PS2+ >= 75%, FOLR1 IHC

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.

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.

Part ofFolate receptor alpha· FOLR1 All readouts

Folate receptor alpha: what it is and how drugs act on it · animated schematic, not to scale

Target · the protein and the cell it sits on
Drug · antibody, small molecule, cell or radioligand
Effect · signal, damage or kill

In plain words · Folate receptor alpha is a vitamin receptor that ovarian cancer cells carry in large numbers, used as the docking site for the ADC mirvetuximab.

IHC score 1 approval threshold

What it means for a patient

If your ovarian cancer is platinum-resistant and at least three quarters of the cells stain moderately or strongly for folate receptor alpha, mirvetuximab soravtansine is on label. Eye examinations before and during treatment are required because the drug can blur vision. Lower expression does not qualify under the current label.

Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.

Scoring rule

75 percent or more of viable tumour cells with moderate (2+) or strong (3+) membrane staining intensity (PS2+ >= 75 percent) on the VENTANA FOLR1 (FOLR-2.1) RxDx Assay.

“Select patients for the treatment of platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer with ELAHERE based on the presence of FRα tumor expression”
ELAHERE prescribing information

Thresholds used in approvals

Threshold	Drug	Cancer	Regulator	Source
FRα-positive (PS2+ >= 75% on the Ventana FOLR1 assay)	Mirvetuximab soravtansine	Platinum-resistant ovarian cancer	FDA	label

Drugs whose label names it

Mirvetuximab soravtansine

Companion diagnostics (FDA list)

Device	Maker	Indication and sample	Drug	PMA / 510(k)
Ventana FOLR1 (FOLR-2.1) RxDx Assay	Ventana Medical Systems (Roche)	Epithelial Ovarian Cancer, Fallopian Tube Cancer, or Primary Peritoneal Cancer - Tissue	Mirvetuximab soravtansine	P220006 (11/14/2022)

Tests that measure it

VENTANA FOLR1 (FOLR1-2.1) RxDx Assay

Trials that name this readout

Matched on the name and aliases of the readout in the title, setting and summary of each trial; a match is a mention, not proof the readout was an entry criterion.