Leukaemia. Scanning electron micrograph (SEM) showing a lymphoblast (round at centre), immature lymphocyte, in the bone marrow of a patient affected by leukaemia. Leukaemia is a type of cancer characterised by a disorganised proliferation of immature lymphocytes (white blood cells) in the bone marrow, the tissue from which all blood cells originate. This proliferation impairs the production of red blood cells, platelets and other white blood cells. Other organs, such as the brain, liver, testes and brain, may cease to function properly as they become infiltrated with the leukaemic cells. Magnification: x32,000 at 8x10 size.