Pd-L1 Expression In Patients With Metastatic Gastric Cancer In South Korea

1571Background: Data are limited and conflicting regarding programmed death ligand 1 (PD-L1) expression as prognostic of clinical outcomes in patients (pts) with metastatic gastric cancer (mGC) treated with standard of care (SOC). Factors affecting the association between PD-L1 expression and outcomes include type of assay and antibody, scoring system for PD-L1 expression, and method of tissue collection. We analyzed the association between tumor PD-L1 expression and clinical parameters in Korean pts with inoperable mGC. Methods: A retrospective study was performed in 201 pts with inoperable mGC from Yonsei Cancer Center in Seoul, South Korea. Biopsy samples were collected at diagnosis. Tumor PD-L1 expression was measured by IHC using the 22C3 PD-L1 antibody pharmDx kit (Dako North America, Carpinteria, CA, USA). PD-L1 positivity was defined as a combined positive score (CPS) of ≥1%, where CPS is PD-L1+ cells (tumor cells, macrophages, lymphocytes) over the total number of tumor cells, expressed as a perc...