The difference between acute myeloid leukaemia and acute lymphoblastic leukaemia is in the type of blood cell that has become abnormal and caused the leukaemia.

We have lots of different types of blood cells that do different types of jobs in our bodies. In AML a type of cell called a myeloid cell has become abnormal and in ALL the cell causing problems is a lymphoblast.

All our blood cells are made in the bone marrow. They start off as very early immature cells called stem cells. Stem cells can develop into any type of blood cell. The first stage of development for a stem cell is to become either a lymphoid cell or a myeloid cell.

Lymphoid cells start out as immature cells called lymphoblasts and eventually develop into mature white blood cells called lymphocytes. Myeloid cells start out as immature cells called myeloblasts, which in turn go through various stages of development before becoming red cells, platelets or white blood cells.

If the abnormal cancer cell that caused the leukaemia started in an immature lymphoid cell lots of lymphoblasts are made. This is called acute lymphoblastic leukaemia (ALL). If the abnormal cell started off as a myeloid cell lots of immature myeloid cells, or myeloblasts, are made. This is called acute myeloid (or myeloblastic) leukaemia, (AML).

Doctors can tell which type of leukaemia someone has by looking at samples from their blood and bone marrow under the microscope and by carrying out special tests on the leukaemia cells. Knowing whether a person has AML or ALL is very important as the treatment is different for each disease. Although both types of leukaemia are treated with chemotherapy the types of drugs and how they are given is different.