The prognostic value of FISH as an adjunct to conventional cytogenetics for the detection of cryptic gene rearrangements on chromosome 16. A retrospective investigation of 13 patients from Northern Ireland diagnosed with M4Eo acute myeloid leukaemia.

M4Eo acute myeloid leukaemia (AML) patients with the typical chromosome 16 abnormalities have a favourable prognosis. These subtle 16q22 gene rearrangements can be difficult to detect by conventional cytogenetic methods and if missed could lead to the incorrect assignment of prognostic group and hence subsequent treatment strategies. We retrospectively studied 13 patients diagnosed with M4Eo AML for such chromosome 16 abnormalities comparing conventional cytogenetic (G-banding) and molecular (FISH) methods. G-banded analysis detected only 2 patients with definite chromosome 16 abnormalities whereas FISH detected 4 patients, one with the typical inversion and three with the typical chromosome 16 translocation. FISH analysis also confirmed a false +ve G-banded result in one patient and a false -ve G-banded result in another patient. Finally, FISH confirmed a deletion of one chromosome 16 homologue in another patient indicating a poor prognosis. The overall survival of patients with the typical 16q22 rearrangements (n=4) was also significantly better (P=0.007) than patients with normal chromosome 16 homologues or having other numerical and/or structural abnormalities (n=9). This set of data shows that FISH is a more accurate method for the detection of cryptic 16q22 gene rearrangements and because of the prognostic implications has become a mandatory test along with conventional cytogenetics for all newly diagnosed M4Eo AML patients in Northern Ireland.