Acute lymphoblastic leukaemia (ALL) is caused by the abnormal division of bone marrow stem cells – which damage the controlling genes of the cells – and a reduction in the number of normal cells. These immature cells, usually referred to as blast cells, do not function properly.
ALL is the most common type of leukaemia in children. It also occurs in adolescents and adults but with less frequency. The disease can appear suddenly and progress rapidly.