# Gene expression

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

## TL;DR

How much a gene is switched on, and therefore how much of its protein a cell makes. Cancer cells often express the wrong genes at the wrong levels.

## Summary

Expression is controlled by switches in the DNA, by chemical marks on the DNA and its packaging (epigenetics), and by signals from outside the cell. Saying a tumour 'expresses HER2' or 'is PD-L1 positive' means the protein is present at a detectable level, usually measured by immunohistochemistry or RNA sequencing. Expression matters for treatment because antibody drugs and ADCs need enough target protein on the cell surface to bind, and because expression signatures (Oncotype DX, PAM50) predict how a tumour will behave.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: expression; expressed; expresses; expression level; expression levels; highly expressed; low expression; high expression

## Sources

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

## Connected records

- terms: [Biomarker](https://onco.cc/terms/biomarker/), [Gene](https://onco.cc/terms/gene/), [Immunohistochemistry (IHC)](https://onco.cc/terms/ihc/), [Interferon-gamma gene signature (T-cell-inflamed signature)](https://onco.cc/terms/interferon-gamma-signature/), [Overexpression](https://onco.cc/terms/overexpression/), [Protein](https://onco.cc/terms/protein/), [RNA](https://onco.cc/terms/rna/), [Uveal melanoma prognostic markers (GNAQ/GNA11, monosomy 3, gene-expression class)](https://onco.cc/terms/uveal-melanoma-prognostic-markers/)
- technologies: [Epigenetic drugs (HDAC, DNMT, EZH2, IDH, menin, BET)](https://onco.cc/technologies/epigenetic-drugs/), [Histopathology & immunohistochemistry](https://onco.cc/technologies/histopathology-ihc/), [RNA sequencing & expression profiling](https://onco.cc/technologies/rna-seq/), [scFoundation (BioMap)](https://onco.cc/technologies/scfoundation/)

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