# Pharmacogenomic testing before chemotherapy

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

## TL;DR

Testing a patient's inherited genes before certain chemotherapies to spot people who cannot break the drug down and would suffer severe, sometimes fatal, side effects.

## Summary

Germline variants alter how patients handle several cancer drugs. DPYD variants reduce dihydropyrimidine dehydrogenase and cause severe toxicity with fluorouracil and capecitabine; UGT1A1*28 raises irinotecan toxicity; TPMT and NUDT15 variants make thiopurines dangerous. Pre-treatment DPYD testing is required or recommended across much of Europe and by the NHS, and dose reduction guided by genotype has been shown to cut severe toxicity; matched comparisons of survival in DPYD and UGT1A1 carriers given reduced doses have not found it shortened overall.

## Fields

- Kind: Technology
- Status: established
- Last checked: 2026-10-20
- Tags: precision
- Principle: Genotype defined variants from blood or saliva and adjust starting doses according to consortium guidelines such as those of the Clinical Pharmacogenetics Implementation Consortium.
- Strengths: Prevents severe and fatal toxicity; Cheap, once-per-lifetime test; Guideline-backed dose tables
- Limitations: Covers only known variants and ancestries unevenly; Turnaround can delay treatment; Uptake outside Europe remains patchy

## Sources

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

## Connected records

- technologies: [DPYD genotyping and DPD phenotyping before fluoropyrimidines](https://onco.cc/technologies/dpyd-genotyping/), [Pharmacokinetic and pharmacodynamic modelling](https://onco.cc/technologies/pkpd-modelling/), [Quantitative systems pharmacology (QSP)](https://onco.cc/technologies/quantitative-systems-pharmacology/), [TPMT and NUDT15 genotyping before thiopurines](https://onco.cc/technologies/tpmt-nudt15-genotyping/), [UGT1A1 genotyping before irinotecan](https://onco.cc/technologies/ugt1a1-genotyping/)
- fronts: [Chemotherapy](https://onco.cc/fronts/chemotherapy/), [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- drugs: [Capecitabine](https://onco.cc/drugs/capecitabine/), [Fluorouracil (5-FU)](https://onco.cc/drugs/fluorouracil/), [Irinotecan (and liposomal irinotecan)](https://onco.cc/drugs/irinotecan/)
- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/)
- ideas: [Test DPYD, UGT1A1 and TPMT/NUDT15 before the first dose, everywhere](https://onco.cc/ideas/idea-tr1-pre-emptive-pharmacogenomic-testing/)
- roadmaps: [Precision roadmap: margins measured in millimetres → tests that find a target → doses fitted to the person → precision that changes outcomes](https://onco.cc/roadmaps/precision-roadmap/)
- terms: [Pharmacogenomics](https://onco.cc/terms/pharmacogenomics-term/)

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