The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells. Although cells in different parts of the body may look and work differently, most repair and reproduce themselves in the same way. Normally, this division of cells takes place in an orderly and controlled manner but if, for some reason, the process gets out of control the cells will continue to divide, developing into a lump which is called a tumour .
Tumours can be either benign or malignant .
In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. If they continue to grow at the original site, however, they may cause a problem by pressing on the surrounding organs. A malignant tumour consists of cancer cells which have the ability to spread beyond the original site, and if left untreated may invade and destroy surrounding tissues. When these cells reach a new site they may go on dividing and form a new tumour, often referred to as a secondary or a metastasis . Doctors can tell whether a tumour is benign or malignant by examining a small sample of cells under a microscope.