{"entity":{"id":"her2-ihc-0","kind":"biomarker","name":"HER2 IHC 0 (HER2-negative, including ultralow)","aka":["HER2 IHC 0","HER2 0","IHC 0","HER2-negative IHC","HER2 null","IHC 0 with membrane staining"],"tldr":"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.","summary":"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.","asOf":"2026-09-23","links":[{"label":"ENHERTU prescribing information (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7e67e73e-ddf4-4e4d-8b50-09d7514910b6"},{"label":"ASCO/CAP HER2 testing in breast cancer guideline, 2018 focused update (Wolff et al., J Clin Oncol)","url":"https://doi.org/10.1200/JCO.2018.77.8738"}],"tags":["biomarker","her2"],"related":["her2-ultralow","her2-ihc-1-plus","her2-low-ihc"],"cancers":["breast-cancer","her2-low-metastatic-breast-cancer","breast-hr-positive","tnbc"],"sections":[],"technologies":[],"targets":[],"drugs":["trastuzumab-deruxtecan","her2-testing-assays"],"companies":[],"institutions":[],"pathways":[],"terms":["her2-low","ihc"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"target":"her2","measurement":"ihc-score","scoringRule":{"text":"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.","quote":"HER2-ultralow (IHC 0 with membrane staining) breast cancer","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7e67e73e-ddf4-4e4d-8b50-09d7514910b6","sourceLabel":"ENHERTU prescribing information; scoring band from the ASCO/CAP 2018 guideline"},"thresholds":[{"value":"IHC 0 with membrane staining (ultralow), HR-positive","drugId":"trastuzumab-deruxtecan","cancerId":"her2-low-metastatic-breast-cancer","regulator":"FDA","source":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7e67e73e-ddf4-4e4d-8b50-09d7514910b6","quote":"Select patients for treatment of unresectable or metastatic HER2-low (IHC 1+ or IHC 2+/ISH-) or HER2-ultralow (IHC 0 with membrane staining) breast cancer with ENHERTU based on HER2 expression","status":"current"}],"tests":[],"assays":["her2-herceptest","her2-pathway-4b5"],"companionDiagnostics":[{"device":"PATHWAY anti-Her2/neu (4B5) Rabbit Monoclonal Primary Antibody","maker":"Ventana Medical Systems (Roche)","drugs":["trastuzumab-deruxtecan"],"indication":"Breast Cancer - Tissue","pma":"P990081/S055 (01/27/2025)","source":"https://www.fda.gov/medical-devices/in-vitro-diagnostics/list-cleared-or-approved-companion-diagnostic-devices-in-vitro-and-imaging-tools"}],"forPatient":"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."},"route":"/biomarkers/her2-ihc-0/","neighbours":{"biomarker":[{"id":"her2-ihc-1-plus","kind":"biomarker","name":"HER2 IHC 1+","route":"/biomarkers/her2-ihc-1-plus/"},{"id":"her2-ihc-3-plus","kind":"biomarker","name":"HER2 IHC 3+ (HER2-positive by immunohistochemistry)","route":"/biomarkers/her2-ihc-3-plus/"},{"id":"her2-low-ihc","kind":"biomarker","name":"HER2-low (IHC 1+ or IHC 2+/ISH-negative)","route":"/biomarkers/her2-low-ihc/"},{"id":"her2-ultralow","kind":"biomarker","name":"HER2-ultralow (IHC 0 with membrane staining)","route":"/biomarkers/her2-ultralow/"}],"cancer":[{"id":"breast-cancer","kind":"cancer","name":"Breast cancer (all types)","route":"/cancers/breast-cancer/"},{"id":"her2-low-metastatic-breast-cancer","kind":"cancer","name":"HER2-low and HER2-ultralow metastatic breast cancer","route":"/cancers/her2-low-metastatic-breast-cancer/"},{"id":"breast-hr-positive","kind":"cancer","name":"HR-positive / HER2-negative breast cancer","route":"/cancers/breast-hr-positive/"},{"id":"tnbc","kind":"cancer","name":"Triple-negative breast cancer (TNBC)","route":"/cancers/tnbc/"}],"drug":[{"id":"her2-testing-assays","kind":"drug","name":"HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH)","route":"/drugs/her2-testing-assays/"},{"id":"trastuzumab-deruxtecan","kind":"drug","name":"Trastuzumab deruxtecan","route":"/drugs/trastuzumab-deruxtecan/"}],"term":[{"id":"her2-low","kind":"term","name":"HER2-low and HER2-ultralow","route":"/terms/her2-low/"},{"id":"ihc","kind":"term","name":"Immunohistochemistry (IHC)","route":"/terms/ihc/"}],"target":[{"id":"her2","kind":"target","name":"HER2","route":"/targets/her2/"}]}}