Leukaemia. Coloured transmission electron micrograph (TEM) of a blood smear from a patient with leukaemia. Leukaemia is a type of cancer that affects the bone marrow and white blood cells (leucocytes, blue), disrupting the levels of normal, healthy blood cells and resulting in damage to the immune system and anaemia (among other symptoms). Here, the nuclei (green and black) of the white blood cells are somewhat deformed.