The main characteristics of benign and malignant tumours.

The idea

A tumour is a mass of cells produced by uncontrolled mitosis. Benign and malignant tumours differ in ways you can be asked to compare. Benign tumours grow slowly and remain compact, usually surrounded by a capsule of fibrous tissue. Their cells are differentiated, resembling normal cells with normal-sized nuclei. Because they do not invade, surgical removal is usually a permanent cure. They can cause harm by pressing on an organ, causing blockages, or releasing excess hormones. Malignant tumours grow rapidly, are irregular in shape and lack a capsule, so they invade surrounding tissue. Their cells are undifferentiated, with large, dark nuclei, and can spread (metastasise).

What earns the marks

• A benign tumour growing slowly and a malignant tumour growing rapidly, both by uncontrolled mitosis.
• Benign cells being differentiated, while malignant cells are undifferentiated with large, dark nuclei.
• The benign tumour being surrounded by a capsule so it stays in one place and does not invade surrounding tissue.
• Malignant cells breaking off and spreading in the blood or lymph to form secondary tumours, that is metastasis.
• Benign tumours usually being cured by removal whereas malignant tumours frequently recur.

Common mistakes and how to put them right

• Stating that benign tumours are harmless, when they can compress an organ, cause blockages or secrete excess hormone.

• Saying benign tumours 'are not cancerous' without giving a structural or behavioural difference.

• Describing spread vaguely as 'moving through the body' without naming the blood or lymph.

• Writing that tumour cells divide by meiosis rather than mitosis.

Exam tips

• Answer comparison questions in pairs: name the feature, then give both tumour types in the same sentence.
• Use the terms differentiated, capsule and metastasis when comparing tumour types.
• If the question gives a micrograph, comment on nucleus size and cell shape rather than guessing from the caption.