Leukaemia is when the bone marrow that makes white blood cells does not work properly. These abnormal white blood cells do not fight infections in the body like they should. The abnormal blood cells build up in a part of our bodies such as the chest and this makes the area swell. There are four main types of Leukaemia. Acute lymphoblastic leukaemia, acute myeloblastic/myeloid leukaemia, chronic lymohocytic leukaemia and chronic myeloid leukaemia.