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ER status is whether the tumour's cells carry the oestrogen receptor, read by staining nuclei. One percent or more of stained nuclei is positive and means hormone-blocking treatment can work; 1 to 10 percent is 'low positive' and behaves more like negative.
The ASCO/CAP 2020 guideline calls a breast cancer ER-positive when at least 1 percent of tumour cell nuclei stain by validated immunohistochemistry, ER-negative below 1 percent, and introduces 'ER low positive' for 1 to 10 percent with a comment that these tumours often behave like ER-negative disease. Every endocrine therapy label (tamoxifen, aromatase inhibitors, fulvestrant) and the CDK4/6 inhibitor, PI3K, AKT and oral SERD labels are written for hormone-receptor-positive or ER-positive disease without restating the 1 percent rule, so the guideline threshold is what laboratories apply. The same 1 percent rule is used for the progesterone receptor.
In plain words · The hormone switch that drives most breast cancers. Blocking or destroying it is the oldest and most effective targeted therapy.
If 1 percent or more of your tumour cells stain for the oestrogen receptor, the cancer is ER-positive and hormone-blocking drugs (tamoxifen, aromatase inhibitors, fulvestrant) are part of treatment, usually with a CDK4/6 inhibitor when the cancer has spread. A result between 1 and 10 percent is 'low positive'; your team may treat it more like ER-negative disease and discuss chemotherapy.
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.
ER-positive: at least 1 percent of tumour cell nuclei stain positive by IHC. ER low positive: 1 to 10 percent. ER-negative: less than 1 percent or no staining, with internal and external controls behaving as expected.
“ER-positive... if ≥ 1% of tumor cell nuclei are immunoreactive”
ASCO/CAP estrogen and progesterone receptor testing guideline, 2020 update (Allison et al., J Clin Oncol)| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| ER-positive (guideline >= 1% nuclei) | Elacestrant | HR-positive / HER2-negative breast cancer | FDA | label |
| Hormone receptor-positive (guideline >= 1% nuclei) | Alpelisib | HR-positive / HER2-negative breast cancer | FDA | label |
| Hormone receptor-positive (guideline >= 1% nuclei) | Capivasertib | HR-positive / HER2-negative breast cancer | FDA | label |
Also defined by ASCO/CAP estrogen and progesterone receptor testing guideline, 2020 update (Allison et al., J Clin Oncol).
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 ESR1 mutation (ligand-binding domain, usually in ctDNA), Alpelisib, Capivasertib, HR-positive metastatic breast cancer after CDK4/6 inhibitors and the tag biomarker.
Shares Capivasertib, Endometrial cancer, HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Capivasertib, Immunohistochemistry (IHC), Endometrial cancer, HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), Breast cancer (all types), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), Breast cancer (all types), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), Breast cancer (all types), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Immunohistochemistry (IHC), Endometrial cancer and the tag biomarker.
Shares Ribociclib, Letrozole (and other aromatase inhibitors), Abemaciclib, Palbociclib.