Research in cancer immunology is currently accelerating following a series of 
cancer immunotherapy breakthroughs during the last 5 years. Various monoclonal 
antibodies which block the interaction between checkpoint molecules PD-1 on 
immune cells and PD-L1 on cancer cells have been used to successfully treat 
non-small cell lung cancer (NSCLC), including some durable responses lasting 
years. Two drugs, nivolumab and pembrolizumab, are now FDA approved for use in 
certain patients who have failed or progressed on platinum-based or targeted 
therapies while agents targeting PD-L1, atezolizumab and durvalumab, are 
approaching the final stages of clinical testing. Despite impressive treatment 
outcomes in a subset of patients who receive these immune therapies, many 
patients with NSCLC fail to respond to anti-PD-1/PD-L1 and the identification of 
a biomarker to select these patients remains highly sought after. In this 
review, we discuss the recent clinical trial results of pembrolizumab, 
nivolumab, and atezolizumab for NSCLC, and the significance of companion 
diagnostic testing for tumor PD-L1 expression.