# Tumour purity

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

## TL;DR

Tumour purity is the fraction of cells in a sample that are actually cancer cells rather than normal, immune or stromal cells.

## Summary

Aran, Sirota and Butte's pan-cancer analysis of TCGA estimated the proportion of cancer cells in each sample by several methods (pathologist counts, copy number, expression and methylation based estimators) and showed purity varies widely between and within cancer types and confounds molecular comparisons. Bulk sequencing measures the whole mixture, so a low-purity sample can look like a different tumour; models trained on bulk data inherit this.

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: tumour purity; tumor purity; tumour cellularity; tumor cellularity; purity estimate
- Tags: cansim-terms

## Notes

- Listed in the CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme; CanSim page path /terms/tumour-purity.

## Sources

- Aran, Sirota and Butte, Systematic pan-cancer analysis of tumour purity (Nature Communications 2015): https://doi.org/10.1038/ncomms9971

## Connected records

- terms: [Bulk RNA sequencing (RNA-seq) and the full transcriptome](https://onco.cc/terms/bulk-rna-seq/), [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Cell composition confound (tumour versus stroma and immune cells)](https://onco.cc/terms/cell-composition-confound/), [Desmoplasia (tumour stroma)](https://onco.cc/terms/desmoplasia/), [Stroma-rich and desmoplastic tumours in molecular data](https://onco.cc/terms/desmoplastic-stroma-rich/)

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JSON: https://onco.cc/api/v1/entities/tumour-purity.json