# FISH / ISH (in situ hybridisation)

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

## TL;DR

A test that uses glowing DNA probes on a tissue slide to count gene copies or spot rearranged genes inside individual cells, used to confirm HER2 amplification, MYCN in neuroblastoma, or ALK and MYC rearrangements.

## Summary

Fluorescence in situ hybridisation (or chromogenic ISH) shows whether a gene is amplified (extra signals per nucleus, as in HER2 with ratio ≥2.0 or ≥6 copies), deleted (del(17p) in CLL, 1p/19q in oligodendroglioma) or broken and rejoined (break-apart probes for ALK, ROS1, MYC, BCL2, BCL6 in 'double-hit' lymphoma). It works on routine fixed tissue and resolves equivocal IHC 2+ HER2 results. Interphase FISH is standard in myeloma and leukaemia cytogenetics; EBER ISH detects Epstein-Barr virus in tumours. NGS increasingly replaces it for fusions.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: FISH; ISH; in situ hybridisation; in situ hybridization; fluorescence in situ hybridization; fluorescence in situ hybridisation; break-apart FISH; EBER in situ hybridisation; EBER

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Fluorescence_in_situ_hybridization
- Wikipedia: https://en.wikipedia.org/wiki/Fluorescence_in_situ_hybridization

## Connected records

- terms: [1p/19q codeletion](https://onco.cc/terms/1p19q-codeletion/), [B-ALL risk groups (NCI criteria, ETV6::RUNX1, hyperdiploidy, hypodiploidy, iAMP21, IKZF1, CNS status)](https://onco.cc/terms/b-all-cytogenetic-risk/), [CDKN2A/B homozygous deletion](https://onco.cc/terms/cdkn2a-homozygous-deletion/), [CLL-IPI (chronic lymphocytic leukaemia prognostic index)](https://onco.cc/terms/cll-ipi/), [Cytogenetics and karyotype](https://onco.cc/terms/cytogenetics/), [del(5q) (5q- syndrome and lenalidomide response)](https://onco.cc/terms/del5q/), [Ependymoma molecular groups (PF-A, PF-B, ZFTA, YAP1, MYCN)](https://onco.cc/terms/ependymoma-molecular-groups/), [Epstein-Barr virus (EBV) in cancer](https://onco.cc/terms/ebv-term/), [FOXO1 fusion status and IRS group (rhabdomyosarcoma)](https://onco.cc/terms/foxo1-fusion-status/), [Gene amplification and copy-number change](https://onco.cc/terms/gene-amplification/), [Gene fusion](https://onco.cc/terms/gene-fusion/), [HER2 testing in biliary tract cancer (IHC, ISH and NGS)](https://onco.cc/terms/her2-testing-in-biliary-cancer/), [HER2 testing in the UK: reflex ISH, the ratio against the copy number, and where the UK differs from ASCO/CAP](https://onco.cc/terms/her2-testing-uk-breast/), [HER2-positive (IHC 3+ or ISH-amplified)](https://onco.cc/terms/her2-positive/), [Ph-like (BCR::ABL1-like) acute lymphoblastic leukaemia](https://onco.cc/terms/ph-like-all/), [Segmental chromosomal aberrations and ploidy (neuroblastoma)](https://onco.cc/terms/segmental-chromosomal-aberrations/), [SS18::SSX fusion (synovial sarcoma)](https://onco.cc/terms/ss18-ssx-fusion/), [t(11;14), cyclin D1 and SOX11](https://onco.cc/terms/cyclin-d1-t11-14/), [Uveal melanoma prognostic markers (GNAQ/GNA11, monosomy 3, gene-expression class)](https://onco.cc/terms/uveal-melanoma-prognostic-markers/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)
- technologies: [Comprehensive genomic profiling](https://onco.cc/technologies/cgp/), [Histopathology & immunohistochemistry](https://onco.cc/technologies/histopathology-ihc/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Gallbladder cancer](https://onco.cc/cancers/gallbladder/), [Lung cancer (all types)](https://onco.cc/cancers/lung-cancer/), [Non-Hodgkin lymphoma (all types)](https://onco.cc/cancers/non-hodgkin-lymphoma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/), [Prostate cancer](https://onco.cc/cancers/prostate/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- key papers: [Anaplastic lymphoma kinase inhibition in non-small-cell lung cancer](https://onco.cc/key-papers/paper-kwak-crizotinib-alk-nsclc-nejm-2010/), [Assessment of a HER2 scoring system for colorectal cancer: results from a validation study](https://onco.cc/key-papers/paper-valtorta-her2-scoring-colorectal-heracles-mod-pathol-2015/), [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/), [Frequent and focal FGFR1 amplification associates with therapeutically tractable FGFR1 dependency in squamous cell lung cancer](https://onco.cc/key-papers/paper-weiss-fgfr1-amplification-squamous-lung-sci-transl-med-2010/), [HER2 overexpression and amplification as a potential therapeutic target in colorectal cancer: analysis of 3256 patients enrolled in the QUASAR, FOCUS and PICCOLO colorectal cancer trials](https://onco.cc/key-papers/paper-richman-her2-amplification-quasar-focus-piccolo-j-pathol-2016/), [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/), [HER2/HER3 pathway in biliary tract malignancies; systematic review and meta-analysis: a potential therapeutic target?](https://onco.cc/key-papers/paper-galdy-her2-biliary-tract-meta-analysis-cancer-metastasis-rev-2017/), [Identification of the transforming EML4-ALK fusion gene in non-small-cell lung cancer](https://onco.cc/key-papers/paper-soda-eml4-alk-fusion-nature-2007/), [Molecular characterisation of neuroendocrine prostate cancer and identification of new drug targets](https://onco.cc/key-papers/paper-beltran-nepc-aurka-mycn-cancer-discov-2011/), [Recurrent fusion of TMPRSS2 and ETS transcription factor genes in prostate cancer](https://onco.cc/key-papers/paper-tomlins-tmprss2-ets-fusion-science-2005/), [ROS1 rearrangements define a unique molecular class of lung cancers](https://onco.cc/key-papers/paper-bergethon-ros1-rearrangements-lung-jco-2012/), [Updated molecular testing guideline for the selection of lung cancer patients for treatment with targeted tyrosine kinase inhibitors](https://onco.cc/key-papers/paper-lindeman-lung-molecular-testing-guideline-jto-2018/)
- ideas: [Reflex HER2 testing of every advanced gallbladder and extrahepatic biliary cancer](https://onco.cc/ideas/idea-gbc-reflex-her2-testing-advanced-biliary/)
- biomarkers: [1p/19q codeletion](https://onco.cc/biomarkers/1p19q-codeletion-readout/), [9p24.1 alteration of the PD-1 ligand loci](https://onco.cc/biomarkers/pd-ligand-9p24-alteration/), [ALK fusion (ALK-positive)](https://onco.cc/biomarkers/alk-fusion/), [BCL2 rearrangement, t(14;18)](https://onco.cc/biomarkers/bcl2-rearrangement/), [Double-hit and triple-hit: MYC with BCL2 and BCL6 rearrangement](https://onco.cc/biomarkers/double-hit-rearrangement/), [HER2 IHC 2+ (equivocal, reflex to ISH)](https://onco.cc/biomarkers/her2-ihc-2-plus/), [HER2 ISH amplified (ERBB2 gene amplification)](https://onco.cc/biomarkers/her2-ish-amplified/), [HER2-low (IHC 1+ or IHC 2+/ISH-negative)](https://onco.cc/biomarkers/her2-low-ihc/), [MET amplification (gene copy number)](https://onco.cc/biomarkers/met-amplification-readout/), [MYCN amplification](https://onco.cc/biomarkers/mycn-amp/), [TMPRSS2-ERG fusion (and the other ETS rearrangements)](https://onco.cc/biomarkers/tmprss2-erg-fusion/), [TP53 mutation and del(17p)](https://onco.cc/biomarkers/tp53-del17p/)
- drugs: [HER2 IHC and ISH companion assays (HercepTest, PATHWAY 4B5, HER2 Dual ISH)](https://onco.cc/drugs/her2-testing-assays/), [UroVysion Bladder Cancer Kit](https://onco.cc/drugs/urovysion/)
- targets: [MYCN (N-myc)](https://onco.cc/targets/mycn/)

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