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IHC 2+ is the in-between HER2 result: moderate staining that cannot be called positive or negative by eye, so the laboratory runs an ISH gene test. 2+ with amplification is HER2-positive; 2+ without it is HER2-low.
A 2+ score is weak to moderate complete membrane staining in more than 10 percent of tumour cells (or intense complete staining in 10 percent or fewer) and is equivocal under ASCO/CAP; reflex in situ hybridisation decides. The result matters twice over: IHC 2+/ISH+ counts as HER2-positive for trastuzumab, pertuzumab, trastuzumab emtansine and trastuzumab deruxtecan, while IHC 2+/ISH- is one of the two HER2-low categories for trastuzumab deruxtecan after chemotherapy (DESTINY-Breast04) or after endocrine therapy (DESTINY-Breast06). In gastric cancer the trastuzumab label defines positivity as IHC 3+ or IHC 2+ with a positive ISH.
In plain words · A growth-signal receptor. Some cancers make far too much of it, and drugs that block it or use it as a docking site have transformed those cancers.
A 2+ result is not final. Your pathologist should run an ISH gene test on the same sample: if the HER2 gene is amplified the cancer is HER2-positive and trastuzumab-based treatment applies; if it is not, the cancer is HER2-low, which in breast cancer opens trastuzumab deruxtecan after earlier treatment.
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.
2+: weak to moderate complete membrane staining in more than 10 percent of tumour cells, or intense complete staining in 10 percent or fewer; classified equivocal and reflexed to in situ hybridisation.
“HER2-low (IHC 1+ or IHC 2+/ISH-) breast cancer, as determined by an FDA-authorized test”
ENHERTU prescribing information; scoring band from the ASCO/CAP 2018 guideline| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| IHC 2+/ISH+ (HER2-positive) | Trastuzumab deruxtecan | HER2-positive gastric cancer | FDA | label |
| IHC 2+/ISH- (HER2-low) | Trastuzumab deruxtecan | HER2-low and HER2-ultralow metastatic breast cancer | FDA | label |
| Device | Maker | Indication and sample | Drug | PMA / 510(k) |
|---|---|---|---|---|
| PATHWAY anti-Her2/neu (4B5) Rabbit Monoclonal Primary Antibody | Ventana Medical Systems (Roche) | Breast Cancer - Tissue | Trastuzumab deruxtecan | P990081/S047 (09/30/2022) |
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.
A direct check of the HERIZON-BTC-01 testing algorithm in routine pathology: IHC 3+ can stand alone, 2+ needs ISH, and the low-level amplification in weakly stained tumours is the group where HER2 drugs are least likely to help.
One cancer page on OnCo cites this paper by its DOI; this record gives the citation a page of its own so a reader can follow it without leaving OnCo. Read the abstract above alongside the citing page listed under Related; the record was created automatically from the Europe PMC entry and its figures have not been checked by hand.
Shares HER2 IHC 1+, HER2-low (IHC 1+ or IHC 2+/ISH-negative), HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2 IHC 3+ (HER2-positive by immunohistochemistry) and the tags biomarker, her2.
Shares HER2-low (IHC 1+ or IHC 2+/ISH-negative), HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2 IHC 3+ (HER2-positive by immunohistochemistry), HER2-low and HER2-ultralow metastatic breast cancer and the tags biomarker, her2.
Shares HER2 ISH amplified (ERBB2 gene amplification), HER2 testing in biliary tract cancer (IHC, ISH and NGS), HER2 IHC 3+ (HER2-positive by immunohistochemistry), Trastuzumab deruxtecan and the tags biomarker, her2.
Shares HER2 status in extrahepatic cholangiocarcinoma and gallbladder carcinoma: concordance between immunohistochemistry and chromogenic in situ hybridization in 140 cases, Zanidatamab for HER2-amplified, unresectable, locally advanced or metastatic biliary tract cancer (HERIZON-BTC-01): a multicentre, single-arm, phase 2b study, HER2-positive (IHC 3+ or ISH-amplified), FISH / ISH (in situ hybridisation).
Shares HER2 IHC 3+ (HER2-positive by immunohistochemistry), Immunohistochemistry (IHC) and the tag biomarker.
Shares HER2 testing in biliary tract cancer (IHC, ISH and NGS), HER2 IHC 3+ (HER2-positive by immunohistochemistry), FISH / ISH (in situ hybridisation), Immunohistochemistry (IHC).
Shares HER2-low (IHC 1+ or IHC 2+/ISH-negative), HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2-low and HER2-ultralow, Immunohistochemistry (IHC).
Shares HER2-low (IHC 1+ or IHC 2+/ISH-negative), HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2-low and HER2-ultralow metastatic breast cancer, HER2-low and HER2-ultralow.