About acute lymphoblastic leukaemia (ALL)
Leukaemia is a cancer of the white blood cells. White blood cells help to fight infection.
There are two different types of white blood cell – lymphoid cells (also known as lymphocytes) and myeloid cells. Normally these cells, which are produced in the bone marrow, repair and reproduce themselves in an orderly and controlled way. In leukaemia, however, the process gets out of control and the cells continue to divide but do not mature.
Acute lymphoblastic leukaemia is an overproduction of immature lymphoid cells, called lymphoblasts or blast cells.
Immature lymphoid cells fill up the bone marrow and stop it making healthy blood cells. As these cells are immature, they cannot work properly. This puts the child at increased risk of infection. Symptoms of leukaemia in children such as bruising and anaemia are caused by the bone marrow’s inability to make enough healthy red blood cells and platelets.
There are several types of childhood acute lymphoblastic leukaemia. These are identified according to the type of lymphoid cell affected and the stage during its development at which it becomes leukaemic:
- The affected lymphocytes may be either precursor(>98 per cent) or mature
- Precursor cell leukaemias may involve either of the two types of lymphocyte: B-cells(87 per cent) or T-cells (13 per cent)
- Precursor B-cell ALL is further divided into three categories: null-cell, common ALLand pre-B ALL
- Common ALL is the most common type of childhood ALL, accounting for up to 70 per cent of cases
Knowing the type of ALL is important as it helps doctors work out the best treatment.
ALL accounts for almost 80 per cent of all childhood leukaemias and around 25 per cent of all childhood cancers with around 400 new cases diagnosed every year in the UK.
There is a peak in incidence of acute lymphoblastic leukaemia in children aged two to three years; more than half of all children diagnosed with acute lymphoblastic leukaemia are under the age of five years.
Boys have a greater risk than girls of developing ALL, by a factor of 4:3. The reason for this difference between the sexes is not known. Boys also require a longer duration of treatment (see below).
Until the 1960s, childhood leukaemia was incurable. Today, thanks to improvements in care and sustained investment in research, the outlook for young patients diagnosed with ALL is good, with a survival rate of over 90 per cent.
Of the different types of ALL, children with so-called common ALL have the best prognosis.
Acute lymphoblastic leukaemia survival rate is highest in children diagnosed between one and four years of age.
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