HER2 mutations are detected via which two methods?

• A. IHC and FISH
• B. IHC and RT-PCR
• C. FISH and RNA-Seq
• D. PCR and NGS

Answer: (A)

HER2 status is determined by looking at two different aspects: the amount of HER2 protein on tumor cell surfaces and the number of HER2 gene copies in the cells. Immunohistochemistry uses antibodies to stain the HER2 protein, giving a semiquantitative score of protein expression. Fluorescence in situ hybridization uses fluorescent probes to count HER2 gene copies and assess amplification. Together, these tests identify cases with protein overexpression and/or gene amplification, which guide eligibility for HER2-targeted therapies. In practice, IHC is used first to screen; if the result is equivocal (a 2+ score), FISH is performed to confirm amplification. While sequencing-based methods can detect HER2 mutations, the standard clinical determination of HER2 status relies on IHC and FISH. Thus, the two methods are immunohistochemistry and fluorescence in situ hybridization.