Leukaemia. Coloured Scanning Electron Micrograph (SEM) of leukaemic cancer cells (red, at left) and healthy bone marrow cells (brown, at right). Leuk- aemia is a cancer of the blood which results in the over-production of white blood cells in the bone marrow. The cancerous cells here show signs of genetic mutation as they are larger than the healthy cells. The proliferation of white blood cells can cause the production of other types of blood cell in the bone marrow to be impaired. Leukaemia may also cause other organs to stop functioning properly as they are infiltrated by the white blood cells. Magnification: x2500 at 6x4.5cm size.