Acute promyelocytic leukaemia (APML)
What is APML?
Acute promyelocytic leukaemia (APML) is a rare sub-type of acute myeloid leukaemia (AML) and is sometimes referred to as AML M31. APML accounts for only 10% of all AML diagnoses.
In APML, immature abnormal neutrophils (a type of white blood cell) known as promyelocytes accumulate in the bone marrow. These immature cells are unable to mature and function like healthy mature white cells. The accumulation of these immature cells in the marrow inhibits normal cell production, which results in lower numbers of blood cells circulating the body.
APML is most commonly associated with a swapping over (translocation) of chromosomes 15 and 17. This causes parts of a gene from each of these chromosomes to join and create a fusion gene called PML/RARA. In some cases, other chromosomes may translocate and cause a variant APML, but this is quite rare.
How common is APML?
Less than 100 cases of APML are diagnosed in Australia each year.
Who gets APML?
Age is not a significant factor as there is a fairly constant rate of diagnosis across all age groups after the age of 10. APML equally affects both men and women.
What causes APML?
In most cases the causes of APML remain largely unknown but it is thought to result from damage to one or more of the genes that normally control blood cell development. Factors that may put some people at an increased risk include exposure to:
- prior chemotherapy or radiotherapy, although the risk of developing APML following treatment for prior cancer is rare. When it does occur, it is referred to as treatment-related APML.
- bone marrow disease. People with prior diseases of the bone marrow have an increased risk of developing secondary APML. Generally however, those with pre-existing bone marrow disorders develop AML.
There appears to be no increased risk of developing APML as a result of environmental or occupational hazards.
What are the symptoms of APML?
The main symptoms of APML are caused by a lack of normal blood cells. Because APML develops quickly, people usually report feeling unwell for only a short period of time (days or weeks) before they are diagnosed. Common symptoms include:
- persistent tiredness, dizziness, paleness, or shortness of breath when physically active due to a lack of red blood cells or anaemia
- frequent or repeated infections and slow healing, due to a lack of normal white cells, especially neutrophils
- increased or unexplained bleeding or bruising, due to a very low platelet count, or problems with the clotting system.
Serious bleeding abnormalities due to the low platelet count and clotting factors are much more frequent in patients with APML compared with ‘standard’ AML. Patients often present with increased bruising and bleeding from gums or their bowels, and are at an increased risk of bleeding in their brain.
Occasionally people have no symptoms at all and APML is diagnosed during a routine blood test. Some of the symptoms described may also be seen in other illnesses, including viral infections, so it is important to see your doctor so that you can be examined and treated properly.