Davis AA, et al. - The treatment paradigm for advanced cancers has changed across many tumor types with the development of immune checkpoint inhibitors. Despite a subset of patients display encouraging and sometimes durable responses, there are many patients who do not respond. Since tumors adopt the PD-1/PD-L1 axis for immune escape to promote their growth, researchers evaluated the value of PD-L1 as a predictive biomarker, based on all US Food and Drug Administration (FDA) drug approvals of immune checkpoint inhibitors. The primary studies correlated with 45 FDA drug approvals from 2011 until April 2019 were analyzed. They identified approvals across 15 tumor types. Across all approvals, in only 28.9% of cases, PD-L1 was predictive and in the remaining cases, it was either not predictive (53.3%) or not tested (17.8%). The PD-L1 thresholds were variable both within and across tumor types using several different assays, including approvals at the following PD-L1 thresholds: 1, 5, and 50%. Measurement of PD-L1 expression was done in a variable fashion; this was assessed either on tumor cells, tumor-infiltrating immune cells, or both. Findings indicate the limited value of PD-L1 expression as a predictive biomarker and suggest practicing caution while implementing the decision to pursue testing for clinical decision-making.