# Tissue-of-origin signal in tumour data

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

## TL;DR

A tumour's molecular profile is dominated by the organ it came from, so a model can look impressive by recognising the organ and must be judged against a baseline that knows only that.

## Summary

The TCGA Pan-Cancer Atlas classification paper found that cell of origin dominates the molecular clustering of ten thousand tumours across thirty-three types. Expression, methylation and even mutation patterns encode the tissue so strongly that a pan-cancer survival or drug-response model gets much of its apparent accuracy from the tissue label; the honest comparison is a tissue-only or cancer-type-only baseline, and within-type (stratified) metrics. The same signal is what classifiers exploit to assign a primary site to cancers of unknown primary (Wikipedia).

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: organ-of-origin signal; tissue-of-origin signal; tissue of origin; organ of origin; cell-of-origin signal; tissue-only floor; type-only floor
- 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/organ-of-origin-signal.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Cancer_of_unknown_primary_origin
- Hoadley et al., Cell-of-Origin Patterns Dominate the Molecular Classification of 10,000 Tumors from 33 Types of Cancer (Cell 2018): https://doi.org/10.1016/j.cell.2018.03.022
- Wikipedia: https://en.wikipedia.org/wiki/Cancer_of_unknown_primary_origin

## Connected records

- terms: [Accuracy, macro-F1 and confusion matrices](https://onco.cc/terms/accuracy-f1/), [C-index (concordance index), Harrell's and Uno's](https://onco.cc/terms/concordance-index/), [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Clinical covariates (age, stage, nodes, treatment flags)](https://onco.cc/terms/clinical-covariates/), [DNA methylation arrays and beta values (450k, EPIC)](https://onco.cc/terms/methylation-arrays/), [Gene co-expression structure](https://onco.cc/terms/gene-co-expression/)
- cancers: [Cancer of unknown primary (CUP)](https://onco.cc/cancers/cancer-of-unknown-primary/)

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JSON: https://onco.cc/api/v1/entities/organ-of-origin-signal.json