Which testing method is commonly used to identify protein expression such as ER and HER2 in tumor tissue?

Which testing method is commonly used to identify protein expression such as ER and HER2 in tumor tissue?

• A. Genetic sequencing
• B. Ultrasound
• C. Immunohistochemistry (IHC)
• D. CT scan

Answer: (C)

Determining protein expression in tumor tissue is assessed most commonly with immunohistochemistry, which uses labeled antibodies to bind specific proteins in preserved tissue sections. In practice, pathologists apply antibodies against proteins like estrogen receptor (ER) and HER2 to a fixed tumor sample and visualize where and how strongly these proteins are present under a microscope. This approach directly shows whether tumor cells are expressing ER or HER2, which is essential for guiding treatment—ER positivity suggests potential benefit from hormone therapy, while HER2 positivity indicates likely responsiveness to anti-HER2 targeted therapy. Immunohistochemistry is preferred here because it reveals protein presence and localization within the actual tumor cells, providing a practical, tissue-based readout. If results for HER2 are uncertain (equivocal), additional reflex testing with a gene-based method like FISH may be used, but the primary and most widely used method to identify these protein expressions is IHC. Other options like imaging studies (ultrasound, CT) or genetic sequencing do not evaluate protein expression in tumor tissue in the same direct, routine way.

Determining protein expression in tumor tissue is assessed most commonly with immunohistochemistry, which uses labeled antibodies to bind specific proteins in preserved tissue sections. In practice, pathologists apply antibodies against proteins like estrogen receptor (ER) and HER2 to a fixed tumor sample and visualize where and how strongly these proteins are present under a microscope. This approach directly shows whether tumor cells are expressing ER or HER2, which is essential for guiding treatment—ER positivity suggests potential benefit from hormone therapy, while HER2 positivity indicates likely responsiveness to anti-HER2 targeted therapy.

Immunohistochemistry is preferred here because it reveals protein presence and localization within the actual tumor cells, providing a practical, tissue-based readout. If results for HER2 are uncertain (equivocal), additional reflex testing with a gene-based method like FISH may be used, but the primary and most widely used method to identify these protein expressions is IHC. Other options like imaging studies (ultrasound, CT) or genetic sequencing do not evaluate protein expression in tumor tissue in the same direct, routine way.