Test BackgroundFISH involves the application of fluorescent DNA probes specific to genes or genetic regions of interest that highlight abnormalities involving these regions.
Conventional cytogenetic analysis is carried out routinely on diagnostic AML samples, however fluorescence in-situ hybridization (FISH) may also be used at the discretion of the laboratory.
In AML FISH is a useful adjunct to conventional cytogenetic analysis for the detection of a genetically abnormal clone and to assist in devising the most suitable management strategy. Subsequent analysis of follow up samples is used to monitor the effects of treatment and define disease remission.
In cases of AML, FISH is useful in the following scenarios:
• Where a specific genetic subtype is suspected and a rapid result is required
• In cases that are suspected of having an aberration that is known to be cryptic at the level of conventional cytogenetics (eg some rearrangements of MLL)
• In cases where a sample has failed to produce metaphases, or in which the disease cells are suspected of having failed to divide.
If a particular genetic subtype is suspected, please inform the laboratory to initiate a rapid FISH test. At diagnosis, further FISH probes may be applied, including – but not limited to – those in the below list, at the discretion of the laboratory and according to the findings of conventional cytogenetic analysis and other assays within IHMD.
CBFB/MYH11 t(16;16) or inv(16)
MECOM [EVI1] 3q26
Chromosome 8 centromere
Where possible, follow-up samples from patients with abnormal karyotypes are monitored by FISH only, unless frank relapse and/or disease progression are suspected, in which case conventional karyotyping will be performed in the first instance.
Sample Required See notes section
Sample Volume Samples would not be rejected on the basis of small volume, however, 5 mL is ideal.
Turnaround Time See notes section
Bone marrow in cytogenetic transport medium (preferred) or lithium heparin is usually the sample of choice, but peripheral blood in lithium heparin may be suitable if there are circulating blasts and/or a high white blood cell count. EDTA samples are only suitable in cases requiring FISH only (ie follow-up samples from patients with FISH-detectable abnormalities, or blood samples taken at diagnosis for exclusion of a specific gene fusion when a bone marrow sample will shortly follow). If in doubt please use lithium heparin. Samples which are non-sterile, clotted or collected in sodium citrate, fixative or saline are not suitable. To ensure appropriate analysis and interpretation it is important to provide clear and concise clinical information.
Rapid FISH tests (exclusion of specific genetic subtypes at diagnosis): 95% should be reported within 3 working days as a “preliminary result”. The remaining conventional cytogenetic analysis will be included in a final report, including any additional FISH, within 10 calendar days if rapid FISH was negative, or < 21 calendar days if rapid FISH was positive.
• Post treatment follow-up samples are treated as routine; 95% should be reported within 21 calendar days