A tumour is simply a lump of abnormal tissue, and it can be benign or cancerous. Cancer is the disease itself, in which cells grow and divide out of control, often forming tumours. So every cancer can produce a tumour, but not every tumour is cancer.
The core difference
Tumour describes a physical mass; cancer describes the disease process that can cause one.
- tumour — an abnormal mass of tissue, benign or cancerous: The scan revealed a small tumour that doctors wanted to monitor closely.
- cancer — a disease of uncontrolled, abnormal cell growth: Her grandmother is recovering from breast cancer.
How to tell them apart
Think of tumour as the noun for the lump and cancer as the name of the disease that can produce it. A doctor who finds a tumour still needs tests to say whether it is benign, meaning it will not spread, or malignant, meaning it is cancerous.
The mix-up usually comes from how casually the words get swapped in everyday speech. Someone might say a person “has a tumour” when they mean cancer, or vice versa, but in medical use the distinction matters: a benign tumour is not cancer at all, even though it is still a tumour.
