The 2008 WHO Classification of Tumours of the Haematopoietic and Lymphoid Tissues subdivides acute myeloid leukaemia (AML) into a number of categories based upon the cytogenetic abnormalities observed. Therefore, it is no longer possible to diagnose AML on the basis of morphology alone.
Fluorescence in situ hybridisation (FISH) is a valuable adjunct to conventional cytogenetic analysis. It allows the identification of genetic abnormalities in both dividing and non‐dividing cells and reveals cryptic insertions and translocations. Thus, genetic rearrangements may be identified despite failure to produce metaphase spreads for analysis from cultured AML cells.
Cytogenetic analysis of AML identifies chromosomal abnormalities in 55–60% cases. The critical abnormalities associated with a favourable outcome include t(15;17) in acute promyelocytic leukaemia (APL), t(8;21) in AML with maturation and inversion 16 in acute myelomonocytic leukaemia. RT‐PCR also identifies most abnormalities in these disorders but, when there is no clear cytogenetic abnormality, FISH is recommended to detect variant translocations or rearrangements. FISH is also capable of unravelling the complexity of seemingly random chromosome abnormalities and discerning new patterns of genetic gain and loss in AML that may lead, in the future, to the identification of targeted therapies for this increasingly common disorder.