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ESR1 mutations arise in the oestrogen receptor's ligand-binding domain after aromatase inhibitor treatment, letting the receptor work without oestrogen. They are usually found in a blood test and select the oral SERDs elacestrant and imlunestrant.
Mutations between codons 310 and 547 (Y537S, Y537N, D538G, E380Q and others) are acquired under aromatase inhibitors in 30 to 40 percent of metastatic HR-positive breast cancers and are best detected in plasma cell-free DNA because they are subclonal and heterogeneous. Elacestrant (Orserdu, 2023) is labelled for ER-positive HER2-negative ESR1-mutated advanced breast cancer after at least one line of endocrine therapy, as detected by an FDA-authorised test; imlunestrant (Inluriyo, 2025) for the same population; vepdegestrant was added to the Guardant360 CDx claims in 2026. Guardant360 CDx is the listed companion diagnostic for all three. Guidelines recommend repeat plasma testing at each progression because the mutation appears over time.
In plain words · The hormone switch that drives most breast cancers. Blocking or destroying it is the oldest and most effective targeted therapy.
If a blood test finds an ESR1 mutation after your cancer has progressed on an aromatase inhibitor, elacestrant or imlunestrant tablets are on label as the next hormone treatment. The mutation is usually not present at diagnosis, so the blood test is repeated each time the cancer grows; a negative result now does not rule out a positive one later.
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.
An ESR1 missense mutation between codons 310 and 547 (or the listed hotspots E380, V422del, S463, L469, L536, Y537, D538) in plasma cell-free DNA or tumour tissue by sequencing.
“ESR1 missense mutations between codons 310 and 547”
FDA: List of FDA-Authorized Companion Diagnostic Devices| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| ESR1-mutated, after at least one line of endocrine therapy | Elacestrant | HR-positive / HER2-negative breast cancer | FDA | label |
| ESR1-mutated, after at least one line of endocrine therapy | Imlunestrant | HR-positive / HER2-negative breast cancer | FDA | label |
| Device | Maker | Indication and sample | Drug | PMA / 510(k) |
|---|---|---|---|---|
| Guardant360 CDx | Guardant Health | Breast Cancer - Plasma | Elacestrant | P200010/S010 (01/27/2023) |
| Guardant360 CDx | Guardant Health | Breast Cancer - Plasma | Imlunestrant | P200010/S021 (09/25/2025) |
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.
Shares ER status (oestrogen receptor by IHC), HR-positive / HER2-negative breast cancer and the tags biomarker, hormone-receptor.
Shares Circulating tumour DNA (ctDNA) and the tags biomarker, resistance.
Shares Circulating tumour DNA (ctDNA) and the tags biomarker, resistance.
Shares Circulating tumour DNA (ctDNA) and the tags biomarker, resistance.
Shares the tags biomarker, resistance.
Shares the tags biomarker, resistance.
Shares Selective oestrogen receptor degrader (SERD), ESR1 mutation, Elacestrant, HR-positive metastatic breast cancer after CDK4/6 inhibitors.
Shares Imlunestrant, Camizestrant, Elacestrant, Estrogen receptor (ERα).