Clinical Utility of the Combined Positive Score for Programmed Death Ligand-1 Expression and the Approval of Pembrolizumab for Treatment of Gastric Cancer

Regulatory approval of pembrolizumab for treatment of gastric and gastroesophageal junction (G/GEJ) adenocarcinoma required a reproducible scoring method for use of programmed death ligand-1 (PD-L1) protein expression as a companion diagnostic to identify likely responders to therapy.To develop an immunohistochemical scoring algorithm that includes PD-L1 expression for tumor and immune cells, that is, the combined positive score.Four previously...