# Primary tumour

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

## TL;DR

The original tumour where a cancer started. Cancer is named after this site for life: a breast cancer that spreads to the liver is still breast cancer, not liver cancer.

## Summary

The primary defines the cancer's biology, its likely drivers and its treatment, because the spread cells (metastases or secondaries) inherit its identity; a pathologist can usually recognise the origin from the cells' appearance and markers. Local treatments, surgery and radiotherapy, are aimed at the primary and can cure a cancer that has not spread; once distant metastases exist, removing the primary usually no longer cures, though it may still relieve symptoms. In about two percent of cases, the primary is never found (cancer of unknown primary), and genomic profiling is increasingly used to infer where it came from.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: primary tumours; primary tumor; primary tumors; primary site; primary cancer; the primary; site of origin; unknown primary; cancer of unknown primary; secondary tumour; secondary tumours; secondaries; primary cancers

## Sources

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

## Connected records

- terms: [Lesion](https://onco.cc/terms/lesion/), [Metastasis](https://onco.cc/terms/metastasis/), [Stage](https://onco.cc/terms/cancer-stage/), [Systemic versus local therapy](https://onco.cc/terms/systemic-vs-local-therapy/), [TNM staging](https://onco.cc/terms/tnm-staging/)
- pathways: [The metastatic cascade](https://onco.cc/pathways/metastatic-cascade/)
- cancers: [Cancer of unknown primary, favourable subsets](https://onco.cc/cancers/cup-favourable-subsets/), [Cancer of unknown primary, unfavourable (adenocarcinoma and poorly differentiated carcinoma)](https://onco.cc/cancers/cup-unfavourable/)

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