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 ALL samples, in addition to a panel of FISH probes for the rapid investigation of known prognostic markers. Further FISH may also be used at the discretion of the laboratory.
In cases of ALL, FISH is useful in the following scenarios:
• Rapid investigation of prognostic markers at diagnosis that are likely to impact on patient management (ie BCR-ABL1 in adults; and BCR-ABL1 and ETV6-RUNX1 in children)
• Identifying aberrations that are 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.
• To monitor residual disease in a patient previously found to carry a FISH-detectable aberration.
In addition to the mandatory diagnostic panel, further FISH probes may be applied to diagnostic samples, including – but not limited to – those in the below list. This will be at the discretion of the laboratory and according to the findings of conventional cytogenetic analysis or other investigations.
IGH and related partner genes
Chromosome enumeration probes
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