What is the difference between a benign and a malignant tumour?

According to the U.S. National Cancer Institute (NCI), the key difference is whether a tumour can spread. The NCI states that benign tumours do not spread into, or invade, nearby tissues. By contrast, the NCI describes cancerous tumours as spreading into, or invading, nearby tissues and being able to travel to distant places in the body to form new tumours — a process it calls metastasis. The NCI notes that these cancerous tumours may also be called malignant tumours. In short, benign essentially means "not cancer," while malignant means cancer. The NCI also points out a practical difference after treatment: when removed, benign tumours usually don't grow back, whereas cancerous tumours sometimes do. This is general information, not personal medical advice; any tumour or diagnosis should be discussed with a qualified clinician.

Last updated: 2026-07-12

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