Leukaemia is the most common form of cancer in children. It is a blood cancer that affects the white blood cells, which are a really important part of our immune system that fights infection.

This information applies to children and teenagers aged 15 and under, and is therefore not relevant to teenagers and young adults diagnosed with ALL. Information for those over 16 years can be found in our adult ALL pages.

The exception is the information about treatments, as people up to 25 years with ALL may be given the same treatment as young children. This is simply because these treatments have the best results for these patients.

There are two main types of leukaemia in children: acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML). They are diagnosed according to the type of white blood cell affected. ALL is the most common form of childhood leukaemia and affects a type of white blood cells called lymphoid cells.

Making blood

White blood cells are made in the bone marrow – the soft tissue in the middle of our bones where all our blood cells are made. Mother cells, called stem cells, reside here and make every type of blood cell that we need.

Stem cells constantly produce new blood cells to replace old and damaged ones. New cells only leave the bone marrow once they have fully matured. This process is well controlled so that we have just the right amount of each blood cell in our body.

Developing leukaemia

When someone has leukaemia, control of blood cell production breaks down. The stem cells make very large numbers of immature blood cells. In the case of ALL these are abnormal, or cancerous, lymphoid cells. They never mature into proper white blood cells, vital to a healthy immune system, and so people with ALL have an increased risk of infection.

The cancer cells cluster in the bone marrow and prevent other important blood cells from being made. Most of the problems of leukaemia are caused by the lack of normal cells in the blood, rather than the leukaemia cells themselves.

What are the signs and symptoms?