Childhood acute myeloid leukaemia (AML)
What is childhood AML?
Acute myeloid leukaemia (AML) is a type of cancer that affects the blood and bone marrow. AML is not a single disease. It is the name given to a group of leukaemias that develop in the myeloid cell line in the bone marrow. Myeloid cells can become red blood cells, platelets and all white blood cells excluding lymphocytes. AML is sometimes called acute myelocytic, myelogenous or granulocytic leukaemia.
AML is characterised by an overproduction of immature white blood cells, called myeloblasts or leukaemic blasts, but can occasionally occur in the red cell or platelet lines. These cells crowd the bone marrow, preventing it from making normal blood cells. They can also spill out into the bloodstream and circulate around the body. Due to their immaturity they are unable to function properly to prevent or fight infection. Inadequate numbers of red cells and platelets being made by the marrow cause anaemia, easy bleeding, and/or bruising.
Some years ago doctors from America, France, and Britain classified AML into eight different subtypes based on the appearance of the leukaemic cells under the microscope. Each subtype provides information on the type of blood cell involved and the point at which it stopped maturing properly in the bone marrow. This is known as the French-American-British (FAB) classification system.
The current World Health Organisation’s classification system for AML uses additional information obtained from more specialised laboratory techniques, like genetic studies, to classify AML more precisely. This information also provides more reliable information regarding the likely course (prognosis), of a particular subtype of AML, and the best way to treat it.
The most important factor in predicting prognosis in AML is the genetic make-up of the leukaemic cells. Certain cytogenetic changes are associated with a more favourable prognosis than others. This means that they are more likely to respond well to treatment, and may even be cured. Other cytogenetic changes are associated with an average or intermediate prognosis, while others are associated with a poor, or unfavourable prognosis. It is important to note that in most cases of AML, neither ‘good’ nor ‘bad-risk’ cytogenetic changes are found. People with ‘normal’ cytogenetics are also regarded as having an average prognosis.
Some subtypes of AML are associated with specific symptoms. For example, in some subtypes of AML, leukaemic cells can spread from the bloodstream into other parts of the body like the gums, causing swelling and discomfort in this area. Acute promyelocytic leukaemia (APML or M3) is associated with bleeding and abnormalities in blood clotting. APML is treated differently to other types of AML, and usually has a good overall prognosis.
How common is AML in children?
Less than a quarter of acute leukaemia diagnoses in children are AML. Around 50 children (0-14 years) are diagnosed with AML in Australia each year.
Who gets childhood AML?
AML can affect children of any age, and girls and boys are affected equally. ALL is the more common childhood acute leukaemia and AML is more prevalent in adults than ALL.
What causes AML in children?
In most cases the causes of AML remain largely unknown but it is thought to result from damage to one or more of the genes that normally control blood cell development. Research is going on all the time into possible causes of this damage and certain factors have been identified that may put some children at an increased risk. These include:
- siblings of a child diagnosed with AML have a slightly higher risk of being diagnosed with AML themselves. This risk is considered quite small though.
- exposure to very high doses of radiation, although very few people in Australia are exposed to radiation levels high enough to increase their risk of AML
- exposure to industrial chemicals like benzene over a long period and certain types of chemotherapy to treat other cancers
- some congenital disorders are associated with the development of AML, like Down syndrome, Bloom syndrome and Fanconi’s anaemia. In these cases the AML tends to develop in childhood or adolescence. In very rare cases, AML develops because an abnormal gene is passed down from one generation to the next.
- some people with pre-existing blood disorders including certain myelodysplastic syndromes (MDS) and myelofibrosis, aplastic anaemia and paroxysmal nocturnal haemoglobinuria have a higher than average risk of developing AML.
What are the symptoms of AML in Children?
Because AML develops quickly, children are usually unwell for only a short period of time before they are diagnosed (days or weeks). The most common symptoms of AML are caused by a shortage of normal blood cells in the circulating blood. These symptoms include:
- anaemia – a low haemoglobin level in the blood can cause your child to have symptoms of persistent tiredness and fatigue, pale complexion, weakness, dizziness or feeling unusually short of breath when physically active
- increased bleeding or bruising – a very low platelet count can cause bruising for no apparent reason, or excessive or prolonged bleeding following minor cuts or injury. Some children have frequent or severe nosebleeds or bleeding gums. Red or purple flat pinhead sized spots may appear on the skin, especially on the legs. These are called petechiae (‘pe-teekee- a’) and they are caused by tiny bleeds under the skin.
- frequent or repeated infections – with a low white blood count children are more likely to develop frequent or repeated infections. These may present as minor skin infections, a sore throat, sore mouth or slow healing of minor cuts and grazes. They may also develop chest infections (coughing), urinary tract infections (frequent passing of urine with a sensation of burning) and fevers. The leukaemia itself can cause of low grade fever, in the absence of an infection.
- bone pain – bone and/or joint pain is common and results from the marrow being literally ‘stuffed’ with leukaemic cells. Occasionally there may be deposits of leukemic cells in bone itself and this can cause localised pain.
- other symptoms – other symptoms may include swollen lymph nodes (glands), chest pain and abdominal discomfort due to a swollen spleen or liver.
Some of the symptoms described above may also be seen in other illnesses, including viral infections. So, most children with these symptoms don’t have leukaemia. However, it is important to see your doctor if your child has any unusual symptoms, or symptoms that don’t go away so that they can be examined and treated properly.