Tumor vs. Tumour
Cambridge labels “tumour” as UK and “tumor” as US for the same medical noun. This guide treats the choice as a documented spelling convention and does not invent a meaning difference between the variants.
Use “tumor” in standard US spelling and “tumour” in standard UK spelling; the difference is orthographic rather than a medical meaning distinction.
Key details
Choose the right form
| Audience / style | Use | Meaning |
|---|---|---|
| US English | tumor | US spelling. |
| UK English | tumour | UK spelling. |
| Quoted medical source / official title | preserve source spelling | Accuracy can outweigh house-style normalization. |
Quick tests
Regional-style test
Is the document following US or UK spelling?
If yes: Use the matching regional form.
If no: If no style is specified, choose one convention and remain consistent.
Caveat: The variants name the same medical concept; do not invent a clinical distinction between them.
Examples
US style: The scan showed a small tumor.
“Tumor” matches the documented US spelling.
UK style: The scan showed a small tumour.
“Tumour” matches the documented UK spelling.
Further guidance
Core difference
Use “tumor” in standard US spelling and “tumour” in standard UK spelling; the difference is orthographic rather than a medical meaning distinction.
Style Boundary
Choose the spelling that matches the audience, region, or house style, and keep that choice consistent where both forms are accepted.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Tumour — Cambridge Dictionary (opens in a new tab)Cambridge Dictionary · UK tumour and US tumor spelling distinction