Putting the Microenvironment into the Immunotherapy Companion Diagnostic

Abstract A post hoc analysis in advanced gastric cancer showed stronger association of programmed cell death-ligand 1 (PD-L1) with immunotherapy efficacy measured by combined positive score (CPS) compared with tumor cells (TC%). This finding suggests expression in immune cells in the tumor microenvironment increases the value of the companion diagnostic test. See related article by Lei et al., p. 3926