Normally, blood cells are made in the bone marrow in an orderly and controlled way. In acute myeloid leukaemia (AML), this process gets out of control and many abnormal leukaemia cells are made. These cells are immature and aren’t able to develop into normal functioning blood cells. They are sometimes called blast cells.

AML is an overproduction of an early myeloid cell. In most types of AML the leukaemia cells are immature white cells. But, in some less common types of AML, too many immature platelets or immature red blood cells are made.

The immature cells fill up the bone marrow, taking up space that is needed to make normal blood cells. Some leukaemia cells 'spill over' into the blood and circulate around the body in the bloodstream. These leukaemia cells don’t mature, and so don’t work properly. This leads to an increased risk of infection as well as symptoms such as anaemia and bruising caused by fewer healthy red blood cells and platelets being made.