Chronic myeloid leukaemia (CML) is a type cancer that affects the blood and bone marrow. In CML the bone marrow produces too many white cells, called granulocytes. These cells, sometimes called blasts or leukaemic blasts, gradually crowd the bone marrow, interfering with normal blood cell production. They also spill out of the bone marrow and circulate around the body in the bloodstream. Because they are not fully mature, they are unable to work properly to fight infections. Over time, a shortage of red cells and platelets can cause anaemia, bleeding and/or bruising.
CML usually develops gradually, during the early stages of disease, and progresses slowly over weeks or months. It has three phases: the chronic phase, the accelerated phase and the blast phase. These phases are distinguished by the number of blast cells (immature white cells) in the blood and bone marrow, and the severity of symptoms.