# HER2 IHC 0 (HER2-negative, including ultralow)

Source: https://onco.cc/biomarkers/her2-ihc-0/  
OnCo record `her2-ihc-0` (Biomarker). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

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.

## Fields

- Kind: Biomarker
- Last checked: 2026-09-23
- Also known as: HER2 IHC 0; HER2 0; IHC 0; HER2-negative IHC; HER2 null; IHC 0 with membrane staining
- Tags: biomarker; her2

## Sources

- ENHERTU prescribing information (DailyMed): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7e67e73e-ddf4-4e4d-8b50-09d7514910b6
- ASCO/CAP HER2 testing in breast cancer guideline, 2018 focused update (Wolff et al., J Clin Oncol): https://doi.org/10.1200/JCO.2018.77.8738

## Connected records

- biomarkers: [HER2 IHC 1+](https://onco.cc/biomarkers/her2-ihc-1-plus/), [HER2 IHC 3+ (HER2-positive by immunohistochemistry)](https://onco.cc/biomarkers/her2-ihc-3-plus/), [HER2-low (IHC 1+ or IHC 2+/ISH-negative)](https://onco.cc/biomarkers/her2-low-ihc/), [HER2-ultralow (IHC 0 with membrane staining)](https://onco.cc/biomarkers/her2-ultralow/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [HER2-low and HER2-ultralow metastatic breast cancer](https://onco.cc/cancers/her2-low-metastatic-breast-cancer/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- drugs: [HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH)](https://onco.cc/drugs/her2-testing-assays/), [Trastuzumab deruxtecan](https://onco.cc/drugs/trastuzumab-deruxtecan/)
- terms: [HER2-low and HER2-ultralow](https://onco.cc/terms/her2-low/), [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/)
- targets: [HER2](https://onco.cc/targets/her2/)

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