# ICD-O-3 (International Classification of Diseases for Oncology)

Source: https://onco.cc/terms/icd-o-3/  
OnCo record `icd-o-3` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

ICD-O-3 codes every tumour twice: a topography code for where it arose and a morphology code for what kind of cells it is made of and how it behaves.

## Summary

The International Classification of Diseases for Oncology is a domain-specific extension of the ICD for tumour diseases, widely used by cancer registries (Wikipedia; the WHO maintains the third edition). Topography codes (C50.9, breast) and morphology codes (8500/3, invasive ductal carcinoma, malignant) appear in TCGA and SEER clinical tables and are the join key between registries and molecular cohorts. Cancer-type labels in machine-learning datasets should resolve to these codes rather than to project names.

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: ICD-O-3; ICD-O; ICD-O-3 morphology code; ICD-O-3 topography code; morphology code; topography code
- 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/icd-o-3.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/International_Classification_of_Diseases_for_Oncology
- WHO: ICD-O: https://www.who.int/standards/classifications/other-classifications/international-classification-of-diseases-for-oncology
- Wikipedia: https://en.wikipedia.org/wiki/International_Classification_of_Diseases_for_Oncology

## Connected records

- collections: [SEER (Surveillance, Epidemiology, and End Results)](https://onco.cc/collections/seer/)
- terms: [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Mondo disease ontology](https://onco.cc/terms/mondo/), [NCI Thesaurus (NCIt)](https://onco.cc/terms/ncit/), [OncoTree cancer classification](https://onco.cc/terms/oncotree-term/), [TNM staging](https://onco.cc/terms/tnm-staging/)

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