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HER2-ultralow is an IHC 0 result with a trace of membrane staining in a few cells. Since 2025, in hormone-receptor-positive breast cancer that has stopped responding to hormone therapy, it is enough for trastuzumab deruxtecan.
Ultralow is faint, incomplete membrane staining in 10 percent or fewer of tumour cells, a sub-band of the ASCO/CAP 0 score. DESTINY-Breast06 enrolled HER2-low and ultralow HR-positive metastatic breast cancer after endocrine therapy and showed a progression-free survival benefit over chemotherapy; the US label was amended in January 2025 and the FDA companion diagnostic list carries the PATHWAY 4B5 antibody with the detail 'HER2 ultralow expression (IHC 0 with membrane staining)'. Reproducibility between pathologists at this end of the scale is low, which is why re-review of 0 slides is often requested.
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.
If your hormone-receptor-positive breast cancer was scored HER2 0, ask the pathologist whether any membrane staining was seen. If so it is ultralow, and trastuzumab deruxtecan is on label after hormone therapy stops working; if there was none, it is not.
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.
IHC 0 with faint, incomplete membrane staining in 10 percent or fewer of tumour cells; distinguished from IHC 0 with no staining.
“HER2 ultralow expression (IHC 0 with membrane staining)”
FDA: List of FDA-Authorized Companion Diagnostic Devices| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| IHC 0 with membrane staining, HR-positive, after endocrine therapy | 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/S055 (01/27/2025) |
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.
Three-quarters of chemotherapy-naive TNBC would be low or ultralow by the DESTINY-Breast06 definitions, but ultralow is unlabelled in TNBC and carries no prognostic weight.
HER2-low is a drug eligibility label, not a biological subtype, in triple-negative disease; because a third of patients qualify for trastuzumab deruxtecan on a score pathologists disagree about, re-scoring and digital assistance for HER2 0 versus 1+ is a practical gap.
Shares HER2 IHC 0 (HER2-negative, including ultralow), 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 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2 IHC 3+ (HER2-positive by immunohistochemistry), Trastuzumab deruxtecan, HER2 and the tags biomarker, her2.
Shares HER2 IHC 3+ (HER2-positive by immunohistochemistry), Trastuzumab deruxtecan, HER2 and the tags biomarker, her2.
Shares HER2 IHC 3+ (HER2-positive by immunohistochemistry), Immunohistochemistry (IHC) and the tag biomarker.
Shares HER2-low and HER2-ultralow, Immunohistochemistry (IHC), Triple-negative breast cancer (TNBC), HR-positive / HER2-negative breast cancer and the tag biomarker.
Shares Clinical, pathological, and PAM50 gene expression features of HER2-low breast cancer, Reflex re-scoring of HER2 0 versus 1+ with digital assistance so every eligible triple-negative patient reaches trastuzumab deruxtecan, HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH), HER2-low and HER2-ultralow metastatic breast cancer.
Shares Immunohistochemistry (IHC), HR-positive / HER2-negative breast cancer and the tag biomarker.