What Causes Cancer? Benign vs Malignant Tumours

Cancer is caused by changes in cells that lead to uncontrolled growth and division. This produces a mass of abnormal cells called a tumour. Benign tumours remain contained in one area, whereas malignant tumours invade tissues and can spread around the body.

What causes cancer?

Normally, the cell cycle controls when cells grow and divide. Changes to genetic material can disrupt this control, causing cells to divide repeatedly when they should not. The abnormal cells may then form a tumour.

The chance of developing cancer can be increased by risk factors, including:

• lifestyle factors such as smoking
• exposure to carcinogens, including some chemicals and ionising radiation
• inherited genetic risk factors

A carcinogen is something that increases the risk of cancer. A risk factor does not guarantee that someone will develop cancer. Many cancers result from several factors interacting.

Benign and malignant tumours

A benign tumour is a growth of abnormal cells contained in one area, usually within a membrane. It does not invade neighbouring tissues or spread elsewhere.

A malignant tumour is cancerous. Its cells invade nearby tissues. Some may enter the blood, travel to another part of the body and form a new growth called a secondary tumour.

Worked example

A scan shows that a tumour has entered surrounding tissue, and similar cells are later found in the liver.

The tumour is malignant because it has invaded nearby tissue and spread to another organ. The liver growth is a secondary tumour.

Common exam mistake

Do not simply write that a benign tumour is “safe”. Benign tumours do not invade or spread, but their size or location could still cause problems. For a clear comparison, use contained, invades, spreads through the blood and secondary tumour.

Assumption: Higher tier. This content is assessed at both Foundation and Higher tier.