# HER2 testing in biliary tract cancer (IHC, ISH and NGS)

Source: https://onco.cc/terms/her2-testing-in-biliary-cancer/  
OnCo record `her2-testing-in-biliary-cancer` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Bile duct and gallbladder tumours are scored for HER2 with the stomach cancer rules, not the breast ones, and a strong stain (3+) is enough for zanidatamab. A borderline stain (2+) needs a gene-copy test, and a sequencing panel can find both the amplification and the rarer point mutations that a stain misses.

## Summary

Scoring. Biliary series and trials score HER2 immunohistochemistry (IHC) by the gastro-oesophageal adenocarcinoma guideline, which accepts incomplete basolateral membrane staining; HERIZON-BTC-01 enrolled patients with ERBB2 amplification confirmed by in situ hybridisation (ISH) at a central laboratory and analysed IHC 2+ or 3+ as HER2-positive, and the FDA label for zanidatamab requires IHC 3+ on an FDA-authorised test, the Ventana PATHWAY 4B5 antibody (Harding 2023; label quoted on the HER2 IHC 3+ readout page). In 140 resected biliary cancers scored this way, IHC was 0 in 72.9%, 1+ in 12.1%, 2+ in 8.6% and 3+ in 6.4%; every 3+ tumour was amplified on chromogenic ISH, some 2+ and rarely 1+ tumours were also amplified, and the mean ERBB2 to CEP17 ratio was 6.2 in 3+ tumours against 3.9 in amplified 2+ or 1+ tumours (Angerilli 2026). Heterogeneity. HER2 staining involved less than half the tumour cells in many cases (Angerilli 2026) and was heterogeneous in 83% of HER2-positive biliary cancers, with loss of expression in deeper, dedifferentiated invasive areas, so small biopsies can under-call it and larger tissue should be tested where possible (Hiraoka 2020). Amplification versus mutation. ERBB2 alterations in gallbladder cancer split into amplification (8%), kinase or extracellular domain mutations such as S310F/Y (4%), both (1.5%) and fusion (0.4%) (Mondaca 2024; Suryavanshi 2025); IHC and ISH see the amplified tumours, whereas mutations are found only by sequencing and are covered by the separate HER2 mutation readout. Panels and turnaround. Comprehensive genomic profiling panels (FoundationOne CDx, MSK-IMPACT, Tempus xT, TruSight Oncology Comprehensive, Caris) report ERBB2 copy number and mutations alongside MSI, TMB, BRAF, NTRK and FGFR2, which is why guidelines ask for panel testing at diagnosis of advanced biliary cancer; in the NHS the Genomic Test Directory route is cited on the cancer page. Turnaround is faster for IHC (days) than for panel sequencing (typically two to four weeks), so IHC with reflex ISH remains the quickest route to a HER2 answer while the panel runs. Plasma. ctDNA panels detected ERBB2 amplification among the therapeutically relevant alterations in 124 biliary patients (Mody 2019), and 37 Indian cfDNA samples mirrored tissue findings qualitatively though 13 had no variant detected (Suryavanshi 2025).

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: HER2 scoring in biliary cancer; HERIZON-BTC-01 HER2 criteria; HER2 IHC versus ISH in cholangiocarcinoma; ERBB2 amplification by NGS

## Sources

- Harding et al., Lancet Oncol 2023: HERIZON-BTC-01, zanidatamab in HER2-amplified biliary tract cancer: https://doi.org/10.1016/s1470-2045(23)00242-5
- Angerilli et al., Hum Pathol 2026: HER2 IHC and chromogenic ISH concordance in 140 biliary cancers: https://doi.org/10.1016/j.humpath.2026.106234
- Hiraoka et al., Hum Pathol 2020: HER2 status in 454 biliary tract cancers: https://doi.org/10.1016/j.humpath.2020.08.006
- Mondaca et al., JCO Glob Oncol 2024: ERBB2-altered gallbladder cancer in an American and a Chilean cohort: https://doi.org/10.1200/go.24.00090

## Connected records

- biomarkers: [HER2 (ERBB2) activating mutation](https://onco.cc/biomarkers/her2-mutation/), [HER2 IHC 2+ (equivocal, reflex to ISH)](https://onco.cc/biomarkers/her2-ihc-2-plus/), [HER2 IHC 3+ (HER2-positive by immunohistochemistry)](https://onco.cc/biomarkers/her2-ihc-3-plus/), [HER2 ISH amplified (ERBB2 gene amplification)](https://onco.cc/biomarkers/her2-ish-amplified/)
- cancers: [Biliary tract cancer (all types)](https://onco.cc/cancers/biliary-tract-cancer/), [Biliary tract cancer (cholangiocarcinoma)](https://onco.cc/cancers/cholangiocarcinoma/), [Gallbladder cancer](https://onco.cc/cancers/gallbladder/)
- technologies: [Comprehensive genomic profiling](https://onco.cc/technologies/cgp/), [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/)
- targets: [HER2](https://onco.cc/targets/her2/)
- drugs: [FoundationOne CDx / Liquid CDx](https://onco.cc/drugs/foundationone-cdx/), [Guardant360 CDx](https://onco.cc/drugs/guardant360-cdx/), [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/), [Zanidatamab](https://onco.cc/drugs/zanidatamab/)
- terms: [Circulating tumour DNA (ctDNA)](https://onco.cc/terms/ctdna/), [FISH / ISH (in situ hybridisation)](https://onco.cc/terms/fish/), [Gene amplification and copy-number change](https://onco.cc/terms/gene-amplification/), [HER2-positive (IHC 3+ or ISH-amplified)](https://onco.cc/terms/her2-positive/), [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [Next-generation sequencing (NGS)](https://onco.cc/terms/ngs/)
- key papers: [Circulating tumor DNA profiling of advanced biliary tract cancers](https://onco.cc/key-papers/paper-mody-biliary-ctdna-profiling-jco-po-2019/), [Clinical and genomic characterization of ERBB2-altered gallbladder cancer: exploring differences between an American and a Chilean cohort](https://onco.cc/key-papers/paper-mondaca-erbb2-gallbladder-us-chile-jco-go-2024/), [Details of human epidermal growth factor receptor 2 status in 454 cases of biliary tract cancer](https://onco.cc/key-papers/paper-hiraoka-her2-status-biliary-hum-pathol-2020/), [Genomic profiling of Indian gallbladder carcinoma: mutational insights in a high-incidence population](https://onco.cc/key-papers/paper-suryavanshi-indian-gallbladder-genomics-jco-go-2025/), [HER2 status in extrahepatic cholangiocarcinoma and gallbladder carcinoma: concordance between immunohistochemistry and chromogenic in situ hybridization in 140 cases](https://onco.cc/key-papers/paper-angerilli-her2-ihc-cish-biliary-hum-pathol-2026/), [Overexpression of the HER2/neu gene: a new therapeutic possibility for patients with advanced gallbladder cancer](https://onco.cc/key-papers/paper-roa-her2-overexpression-gallbladder-gcr-2014/), [Zanidatamab for HER2-amplified, unresectable, locally advanced or metastatic biliary tract cancer (HERIZON-BTC-01): a multicentre, single-arm, phase 2b study](https://onco.cc/key-papers/paper-harding-lancet-oncol/)

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