Significance of Immunohistochemistry and In Situ Hybridization Techniques for Predictive Biomarker Studies

Abstract

Immunohistochemistry (IHC) and in situ hybridization (ISH) are morphology-based methods which allow direct assignment of findings to the cells of interest, e.g., cancer cells. IHC detects changes of protein expression qualitatively or as a semiquantitative measurement. Reliability of IHC-based predictive biomarkers is highly dependent on pre-analytical factors, selection of suitable antibodies, staining procedures, as well as an assessment of staining. Specific reading and scoring approaches for different tumor entities make evaluations complex, especially for evolving biomarkers in the context of immuno-oncology treatment. ISH assays are basically capable of detecting gene amplifications, large deletions, and gene fusions. Definitions of amplifications are gene and entity specific. Activating rearrangements frequently involve genes encoding receptor tyrosine kinases which can be addressed by tyrosine kinase inhibitors. Most of the currently applied predictive biomarkers are based on either IHC or ISH. The number of assays is steadily growing, and great efforts are needed to achieve and maintain the highest level of reliability. Future developments will introduce multiplexing IHC and ISH.