PDCD1 and colorectal carcinoma: Aside from dMMR/MSI-H, one of the most widely used predictive biomarkers for anti-PD1 therapy is PDL1 IHC; however, conflicting results from studies regarding definitive cut-off thresholds, tumor/ stromal staining and poor inter-reader concordance results mean that it is not routinely used for CRC, thus highlighting that a more robust predictive biomarker approach is required.