The “eyes” have it?—intra- and inter-observer reproducibility of the PD-L1 companion diagnostic assay

The role of the immune system in cancer is well established. Indeed, most potential cancer causing cells are detected and removed from our bodies by our immune system in a process called “immune surveillance”. However, at some point, tumors manage to evade our immune system often by expressing signals that inhibit the anti-tumor immune response (1). “The scientific turning point for cancer immunotherapy came with the understanding that T cell immune responses are controlled through on and off switches, so-called ‘immune checkpoints’ that protect the body from possibly damaging immune responses” (2). Blockade of these checkpoints has emerged as a new paradigm for the treatment of a cancer, including NSCLC (3).