Harmonization of programmed cell death ligand-1 diagnostic assays in non-small cell lung cancer

Targeting the programmed death 1/programmed cell death ligand-1 (PD-1/PD-L1) immune checkpoint pathway in non-small cell lung cancer (NSCLC) with anti-PD-1 and anti-PD-L1 monoclonal antibodies led to durable responses for some patients and signalled to the oncology community that immunotherapy had finally arrived as an important anti-cancer therapy (1,2). Currently more than 200 clinical trials are on-going or actively recruiting targeting at least one aspect of the PD pathway in NSCLC. One of the major challenges in developing these clinical trials has been the need for standardized assays to measure tumoral PD-1 and PD-L1 expression, as a potential predictive biomarker of response (3,4).