Carcinogens and cancer risk

A carcinogen is an agent that increases the risk of cancer. Some carcinogens damage DNA, causing changes in its information called mutations.

DNA contains information that helps control cell division. If mutations affect this control, cells may divide uncontrollably and form a cancer. Ionising radiation is a physical carcinogen that can cause DNA damage and mutations.

Tobacco smoke contains carcinogenic substances. Exposure to a carcinogen increases the risk of cancer; it does not guarantee that cancer will develop.

Benign and malignant tumours

A tumour is a growth of abnormal cells formed when cells divide uncontrollably. Tumours are classified as benign or malignant according to whether their cells invade nearby tissues and spread.

Benign tumours

A benign tumour remains contained in one area, usually within a membrane. Its cells do not invade neighbouring tissues or spread to other parts of the body.

Malignant tumours

A malignant tumour is a cancer. Its cells invade neighbouring tissues and can enter the blood, which may carry them to other parts of the body. There, they can divide and form secondary tumours.

This spread is called metastasis. A secondary tumour develops from cells of the original cancer, even though it grows in a different part of the body.

Lifestyle and genetic cancer risk

A risk factor is something that increases the likelihood of developing a disease. It does not mean that the disease is certain to occur. Both lifestyle and inherited genetic variants can affect a person’s risk of developing some cancers.

Lifestyle and cancer risk

Lifestyle factors are patterns of behaviour that can change a person’s exposure to carcinogens: agents that can cause cancer. Carcinogens can damage DNA, increasing the chance of changes that disrupt the control of cell growth and division.

Different cancers are associated with different risk factors. For example, smoking increases the risk of lung cancer because tobacco smoke contains carcinogens. Frequent exposure to ultraviolet radiation from the Sun increases the risk of skin cancer.

Inherited genetic susceptibility

A person can inherit a genetic variant that increases their susceptibility to certain cancers. Some inherited variants affect processes that normally control cell growth and division, making it more likely that cells will grow and divide uncontrollably.

Inheriting susceptibility is not the same as inheriting cancer. The variant increases risk, but cancer is not certain to develop. Lifestyle and inherited genetic factors can both contribute to a person’s risk.