Which method can be used to assess HER2 gene amplification when IHC is inconclusive?

Which method can be used to assess HER2 gene amplification when IHC is inconclusive?

• A. Immunohistochemistry (IHC)
• B. FISH
• C. PCR
• D. MRI

Answer: (B)

When IHC results are inconclusive for HER2, the goal is to determine if the tumor actually has HER2 gene amplification to guide therapy. Fluorescence in situ hybridization uses fluorescent DNA probes to visualize and quantify HER2 gene copies directly within the tumor cells on the tissue section. It provides a clear, proportion-based readout, such as a HER2 to CEP17 ratio around or above 2.0 or an average HER2 copy number of about 6 per cell, which indicates amplification. This direct assessment of gene copy number resolves the ambiguity left by an equivocal IHC result and helps decide eligibility for HER2-targeted treatments. Other options either measure protein levels (which don’t resolve gene amplification) or rely on imaging or bulk DNA analysis that can be less reliable in heterogeneous tumors. Hence, FISH is the most appropriate confirmatory test after an inconclusive IHC.

When IHC results are inconclusive for HER2, the goal is to determine if the tumor actually has HER2 gene amplification to guide therapy. Fluorescence in situ hybridization uses fluorescent DNA probes to visualize and quantify HER2 gene copies directly within the tumor cells on the tissue section. It provides a clear, proportion-based readout, such as a HER2 to CEP17 ratio around or above 2.0 or an average HER2 copy number of about 6 per cell, which indicates amplification. This direct assessment of gene copy number resolves the ambiguity left by an equivocal IHC result and helps decide eligibility for HER2-targeted treatments. Other options either measure protein levels (which don’t resolve gene amplification) or rely on imaging or bulk DNA analysis that can be less reliable in heterogeneous tumors. Hence, FISH is the most appropriate confirmatory test after an inconclusive IHC.