Programmed death-ligand 1 (PD-L1) expression has now been implicated in gastric cancer (GC). This study was conducted to determine the impact of clinicopathological characteristics on PD-L1 expression and its association with survival in GC patients receiving standard-of-care. In total, 268 GC patients receiving upfront surgery were enrolled at Chiang Mai University Hospital. PD-L1 expression was assayed by immunohistochemistry staining using the Dako 22C3 pharmDx. The rates of PD-L1 positivity by combined positive score (CPS) at a cutoff value of 1 and 5 were 22% and 7%. PD-L1 positivity was significantly higher in patients younger than 55 than those older than 55 (32.6% vs. 16.5%, p = 0.003; 11.6% vs. 4.4%, p = 0.027). PD-L1 positivity was observed more frequently in GC with metastases than without (25.2% vs. 17.1%, p = 0.112; 7.2% vs. 6.7%, p = 0.673). Patients with PD-L1 positive had a significantly shorter median overall survival than those with PD-L1 negative (32.7 vs. 41.6 months, p = 0.042, 27.6 vs. 40.8 months, p = 0.038). In conclusion, PD-L1 expression has been associated with young age, short survival, and metastases, although unrelated to the tumor stage. For GC patients, PD-L1 testing is recommended, especially among young patients with metastases.
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