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IHC 0 is no HER2 staining, or faint staining in 10 percent or fewer cells. It is HER2-negative, but the label now separates true zero from 'IHC 0 with membrane staining', the ultralow group that trastuzumab deruxtecan can treat in hormone-receptor-positive breast cancer.
The ASCO/CAP 0 band covers no staining and incomplete faint staining in 10 percent or fewer of tumour cells; the guideline treats it as a single negative category. DESTINY-Breast06 split it: tumours with any faint, incomplete membrane staining in 10 percent or fewer cells ('HER2-ultralow') responded to trastuzumab deruxtecan like HER2-low tumours, and the US label was expanded in January 2025 to HER2-low or HER2-ultralow (IHC 0 with membrane staining) HR-positive breast cancer after endocrine therapy. A true 0 with no staining at all remains outside every HER2-directed label. Distinguishing 0 from ultralow at the low end of the scale is the hardest read in HER2 pathology and the reason AI-assisted scoring is being validated.
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 0 result means HER2-directed antibodies such as trastuzumab are not used. If your breast cancer is hormone-receptor-positive, ask whether the 0 was a true zero or 'with membrane staining' (ultralow), because the ultralow group can now receive trastuzumab deruxtecan once hormone therapy has stopped working.
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.
0: no staining, or incomplete faint membrane staining in 10 percent or fewer of tumour cells. 'IHC 0 with membrane staining' (ultralow) is the sub-band with faint incomplete staining in 10 percent or fewer cells.
“HER2-ultralow (IHC 0 with membrane staining) breast cancer”
ENHERTU prescribing information; scoring band from the ASCO/CAP 2018 guideline| Threshold | Drug | Cancer | Regulator | Source |
|---|---|---|---|---|
| IHC 0 with membrane staining (ultralow), HR-positive | 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.
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 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-ultralow (IHC 0 with membrane staining), 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.
Shares HER2 IHC 3+ (HER2-positive by immunohistochemistry), Immunohistochemistry (IHC) and the tag biomarker.
Shares HER2-ultralow (IHC 0 with membrane staining), HER2-low and HER2-ultralow metastatic breast cancer, HER2-low and HER2-ultralow, Immunohistochemistry (IHC).
Shares Immunohistochemistry (IHC), Breast cancer (all types), HR-positive / HER2-negative breast cancer 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.