Relationship between PD-L1 protein expression and gene amplification in gastric cancer tissues

Abstract

Objective: To investigate the relationship of PD-L1 protein expression and gene amplification in gastric cancer and their correlation with clinicopathologic factors. Methods: The cohort included 247 gastric cancer specimens with follow-up data and clinicopathologic data obtained from Shanxi Cancer Hospital in 2011. PD-L1 expression was detected by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). Results: PD-L1 protein was expressed in 25.9% (64/247) of the tumor cells and 26.7% (66/247) of the tumor infiltrating immune cells (IC). There was a correlation between the two (P<0.01). The expression of PD-L1 in tumor cells correlated with the degree of differentiation and tumor diameter(P<0.05). The PD-L1 expression in IC correlated with vascular tumor thrombi(P<0.05). The amplification rate of PD-L1 gene detected by FISH was 19.0% (47/247), and was associated with age, large/small curvature of the stomach, tumor location, tumor diameter, and lymph node metastasis(P<0.05). The positive coincidence rate of the two methods was 25.0% (16/64), negative coincidence rate was 83.0% (152/183), and total coincidence rate was 68.0% (168/247), suggesting that the coincidence of IHC and FISH was poor (P=0.157). There was a negative correlation between PD-L1 protein expression on tumor cells and prognosis in gastric cancer. There was no significant correlation between PD-L1 protein expression on IC and PD-L1 gene amplification with prognosis. Vascular tumor thrombi, tumor diameter, depth of invasion, and lymph node metastasis were all poor prognostic factors of gastric cancer(P<0.05). Multivariate Cox regression analysis showed that PD-L1 protein expression, depth of invasion and lymph node metastasis were all independent prognostic risk factors for gastric cancer. Conclusions: Concordance between PD-L1 protein expression and gene amplification is poor. PD-L1 protein expression may signify poor prognosis. There is no significant correlation between PD-L1 gene amplification and prognosis of patients with gastric cancer.