Programmed Death Ligand-1 Immunohistochemistry: Friend or Foe?

The approval of anti-programmed death receptor (PD)-1 therapies for non-small cell lung cancer has directed the spotlight on programmed death ligand-1 (PD-L1) immunohistochemistry as the latest predictive biomarker potentially required in this disease. Several other drugs in this class will likely be approved in the future and each has been developed with a unique anti-PD-L1 immunohistochemistry test. The prospect of 5 drugs competing in the same treatment area, each possibly requiring PD-L1 immunohistochemistry testing, presents a challenge for pathologists unlike any previously faced. The key issue is whether laboratories will attempt to deliver the trial-validated assays for one or more of these treatments, or introduce instead one or more laboratory developed tests, or attempt to provide a single PD-L1 immunohistochemistry assay for all possible anti-PD-1 and anti-PD-L1 treatments that may be used. This paper discusses some of the issues, challenges, hazards, and possible solutions that have recently emerged in this most complex interface between cancer therapeutics and laboratory biomarker testing.