Leukaemia blood cells. Coloured scanning electron micrograph (SEM) of white blood cells from a patient with chronic lymphocytic leukaemia. This form of cancer is most often found in the elderly, and involves an increase in circulating levels of lymphocytes (a type of white blood cell), as seen here. This causes a reduction in the proportion of red blood cells, leading to anaemia, as well as other complications such as enlargement of the liver and spleen. Magnification: x2000 when printed at 10 centimetres wide.