An update on companion and complementary diagnostic assays for PD-1/PD-L1 checkpoint inhibitors in NSCLC.

: Development within molecular medicine has given us an increased understanding of the pathophysiology of malignant diseases. This understanding has been the key to a development of a number of new effective target-specific drugs, including the PD-1/PD-L1 checkpoint inhibitors.: This review will focus on the clinical validation and utility of the commercially available IHC PD-L1 expression assays linked to the different PD-1/PD-L1 checkpoint inhibitors indicated for treatment of NSCLC. For the discussion of this subject, mainly data from studies where the PD-1/PD-L1 checkpoint inhibitors have been given as monotherapy will be reported.: Although PD-L1 expression is not the perfect biomarker; the different IHC PD-L1 expression assays have had major impact on the clinical development of PD-1/PD-L1 checkpoint inhibitors for treatment of NSCLC. A number of clinical studies in NSCLC have shown that the efficacy of the PD-1/PD-L1 checkpoint inhibitors are positively correlated to the level of PD-L1 expression. Based on studies presented in this review, the recommendation is that monotherapy should mainly be used for treatment of NSCLC patients with a high PD-L1 expression, as defined by the cutoff values for the individual assays linked to the specific PD-1/PD-L1 checkpoint inhibitor.