Cancer is the result of changes in cells that lead to uncontrolled growth and division. Normally the body controls how fast cells divide. In cancer that control is lost, so the cells keep dividing and form a lump of cells called a tumour.
There are two kinds of tumour. A benign tumour is a growth of abnormal cells that stays in one area, usually inside a membrane. It does not invade other parts of the body. A malignant tumour is made of cancer cells. These cells invade neighbouring tissues and spread to different parts of the body in the blood, where they form secondary tumours.
Scientists have identified lifestyle risk factors for various types of cancer. Smoking, a poor diet and lack of exercise are examples. There are also genetic risk factors for some cancers, which means a person can inherit a higher chance of developing them.
