The body is made up of many types of cells, and these cells grow and divide in a controlled way to produce more cells as they are needed to keep the body healthy. When cells become old or damaged, they die and are replaced with new cells.
However, sometimes this organised process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. The extra cells may form a mass of tissue called a tumour. As they begin to get bigger Cancer cells can spread to other parts of the body through the blood and lymph systems thus allowing them to invade parts of the body and affect organs and tissues around them.