Classification of acute myeloid leukaemia (AML)
Acute myeloid leukaemia (AML) can be divided (or classified) into different sub-types. This is important as different types of AML are treated in different ways. Your doctors need to know which type you have to help them plan the most appropriate treatment for you.
Your bone marrow sample will be tested to find out which type of AML you have. Different types of AML are associated with particular genetic changes. So the following tests can help doctors decide on the best treatment and predict how well the leukaemia may respond to it.
This involves testing the leukaemia cells with antibodies to look for specific proteins on their surface. It helps doctors identify what type of cell has become abnormal.
This is the study of chromosomes. Almost all the cells in our bodies contain chromosomes, which are made up of genes. The genes control all the activities of the cell. With leukaemia, there are often changes in the structure of the chromosomes in the leukaemia cells, but not in the normal cells. A cytogenetic test on the bone marrow sample looks for these changes.
FISH (fluorescence in situ hybridisation)
This test is used to look for specific changes in the chromosomes that can’t be seen with cytogenetic testing.
PCR (polymerase chain reaction)
This is a very sensitive test that can identify chromosome changes that are too small to see under a microscope. PCR testing may also be done after treatment to check how well it has worked.
WHO and FAB classification of AML
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In the UK, doctors usually classify AML according to the World Health Organisation (WHO) system and the French American British (FAB) system.
The WHO system classifies AML according to the type of cell that has become abnormal and whether:
there are particular chromosomal changes (cytogenetics)
there are abnormal changes in more than one type of blood cell
the leukaemia has developed from a previous blood disorder called myelodysplasia
the leukaemia is related to previous cancer treatment (treatment-related AML).
The WHO system is important as it’s useful for planning treatment and predicting response.
The FAB system looks at the appearance of the leukaemia cells under a microscope (morphology). Each type of AML is named according to the cell type and given a number from M0–M7. Doctors may classify AML with the FAB system while waiting for the results of other tests.