Cancer is a disease which occurs when changes in a group of normal cells within the body lead to an uncontrolled, abnormal growth forming a lump called a tumour; this is true of all cancers except leukaemia (cancer of the blood). If left untreated, tumours can grow and spread into the surrounding normal tissue, or to other parts of the body via the bloodstream and lymphatic systems, and can affect the digestive, nervous and circulatory systems or release hormones that may affect body function.
Cancer tumours can be divided into three groups: benign, malignant or precancerous
Cancer can be classified according to the type of cell they start from. There are five main types: