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HER2/neu gene FISH

Details of Fluorescent In Situ Hybridization (FISH)

FISH methods detect the HER2 gene copy number using two fluorescent-labeled DNA probes. FISH is less subject to the problems of fixation, storage, antigen preservation, and inter-observer variability than is IHC analysis. Literature has cited FISH methods as capable of 96.5% sensitivity and 100% specificity. However, fluorescent signals are not always clearly defined; clumping of signals occurs, and some cases are undecipherable by FISH for this reason. There is still subjectivity introduced with signal enumeration. In comparisons to IHC analysis, the FISH method is more time-consuming and technically more difficult to perform. Technical assay performance takes approximately 16 hours for FISH, compared with approximately three hours for IHC analysis. Technicians also need to be specially trained for FISH. A pathologist must be involved during the test performance to select the tumor area for analysis. FISH reagent costs are typically at least three times the costs of IHC analysis. Additional considerations with FISH include:
  • Morphology context is obscured and analysis suffers with heterogeneous tumors.
  • Special equipment is needed.
  • Permanent slides are usually not available for review, as signals fade during archival.
  • Despite its excellent specificity, FISH can still be “equivocal.”