PDCD1 and neoplasm: To date, several monoclonal antibodies (mAb) targeting the PD-1/PD-L1 pathway have been approved by the Food and Drug Administration (FDA) including nivolumab and pembrolizumab.13 In these clinical trials, durable responses were observed but only in a subset of patients who were not all identified as positive for PD-L1 expression using immunohistochemistry (IHC) from tumor biopsy tissue.14 Although tumor expression of PD-L1 determined from IHC methods has shown promise as a predictive biomarker for patient selection and therapeutic responses, these IHC results have not been conclusive.