ABSTRACT
This chapter summarizes the state of knowledge on available and promising immune biomarkers, including PD-L1 immunohistochemical stain, mismatch repair, microsatellite instability, tumor mutational burden (TMB), as the companion or complementary diagnostics for selecting candidate cancer patients for ICI therapy. We also discuss several emerging immune biomarkers that are undergoing clinical validation. Multiplexed immunohistochemistry (ICH) can identify multiple biological markers in tumor microenvironment and has become a vital tool for understanding therapeutically response to immune checkpoint inhibitors. Second, the density of immune cell subtypes as well as their relative spatial positioning can be evaluated simultaneously to characterize the complex interplay of multiple biomarkers in the tumor microenvironment. Although much attention is focused on tumor tissues in immune biomarker research, tumor derived biomarkers have shown limitations mainly due to inadequate tumor sampling, invasive procedures or lack of consensus in IHC staining. In addition, the utility of the existing immune biomarkers varies significantly among various immune checkpoint inhibitors, tumor types, and the status of companion versus complementary diagnostics.
