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Fluorescence in Situ Hybridization (FISH): Equivocal Results

  • The CURRENT equivocal range for FISH assays are defined as HER2/CEP17 ratios from <2.0 with an average HER2 copy 4.0 and <6.0 signals/cell.
  • Patients with a HER2/CEP17 FISH ratio between 1.8 - 2.2 were formerly considered HER2-positive and were eligible for treatment in the adjuvant trastuzumab trials.
  • Equivocal results of a single test (IHC or FISH) require additional action. The same specimen can be used for an alternate test or a new test can be performed (new specimen using same or alternate test).
  • Equivocal IHC samples must be confirmed by FISH analysis of the sample.
  • Equivocal FISH samples are confirmed by counting additional cells or repeating the FISH test.
  • If FISH remains equivocal after additional cells counted or assay repeated, confirmatory IHC is recommended so that HER2 protein expression is known for the sample with true equivocal gene amplification.