Acute lymphocytic leukaemia. Light micrograph of cancerous white blood cells (purple) in human acute lymphocytic leukaemia. In this peripheral blood smear, the disease is shown by the abnormally large number of lymphocyte white blood cells among the smaller red blood cells. These immature cancer cells have large nuclei. Lymphocy- tes normally form part of the immune system. The abnormal growth of white blood cells in leukaemia reduces the number of normal blood cells that can be produced, resulting in anaemia, poor blood clotting and a weakened immune system. Treatment includes anti-cancer drugs and bone marrow transplants. Magnification: x400 at 35mm size.