As mutant cells (those with mistakes in their genetic blueprint) grow and divide, a mass of abnormal cells or a tumour is formed. In some cases these cells will form a discrete lump, in other cases such as leukaemia (type of blood cancer), abnormal blood cells circulate around the body. Cancer cells can break away from the mass (or tumour) and travel via the bloodstream or lymphatic system to different parts of the body. These cells can settle in other parts of the body to form a secondary cancer or metastasis.
