Cells normally divide at a rate the body controls. Cancer is the result of changes in cells that lead to uncontrolled growth and division. The cells keep dividing when they should not, and a lump of abnormal cells called a tumour can build up.
Not every tumour is a cancer. A benign tumour is a growth of abnormal cells that is contained in one area, usually within a membrane. Its cells do not invade other parts of the body. The cells of a malignant tumour are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood, where they form secondary tumours.
Scientists have found lifestyle risk factors for many types of cancer, for example smoking. There are also genetic risk factors for some cancers, so a person can inherit a higher chance of developing them.
