Systematic Review of PD-1/PD-L1 Inhibitors in Oncology: From Personalized Medicine to Public Health.

The number of PD-[L]1 inhibitors in drug development and the associated companion and complementary diagnostics have led to regulatory challenges and questions regarding generalizability of trial results. The interchangeability of PD-L1 immunohistochemical assays between PD-1/PD-L1 drugs is unclear. Furthermore, robust responses in some patients with low levels of PD-L1 expression have limited the use of PD-L1 as a predictive biomarker across all cancers, particularly in the setting of diseases with few alternative treatment options. This review summarizes the biomarker thresholds and assays approved as complementary and companion diagnostics and provides regulatory perspective on the role of biomarkers in oncology drug development.