The Predicting Value Of Microsatellite Instability And Epstein Barr Virus Infection Combined With PD-L1 Protein Expression On The Prognosis Of Gastric Cancer

Objectives:Microsatellite instability(MSI)and Epstein-Barr virus(EBV)-positive subtypes,which exhibit complex immune responses,have provided new prognostic and therapeutic implications in gastric cancer(GC).PD-L1(Programmed cell death ligand1)has emerged as a promising prognostic biomarker associated with the cancer immune microenvironment.This study aimed to determine the prognostic value of different molecular subtypes and whether the addition of PD-L1 would accurately predict the prognosis and efficacy of postoperative chemotherapy for GC patients,so as to provide a theoretical basis for the individualized treatment of gastric cancer patients.Methods:The patients enrolled in this study were 226 patients with gastric cancer who were treated in the Department of gastro colorectal surgery of the first hospital of Jilin University from 2010 to 2017.All patients received radical gastrectomy,and their basic information and follow-up information were collected from the information database and follow-up management system.The follow-up information was collected by professional follow-up staffs at 3 months,6 months and every year after tumor resection Telephone follow-up was performed,including treatment,recurrence,progression and death.We performed molecular subtyping of tissue microarray slides from 226 GC patients.The MSI status and PD-L1 expression were evaluated through immunohistochemistry(IHC)and EBV status through in situ hybridization.Multiplex polymerase chain reaction(PCR)was also performed on 50 cases to validate the accuracy of IHC in defining MSI status,and Kappa test was used to analyze the consistency of MSI status by immunohistochemistry and PCR.Kaplan-Meier method was used to draw the survival curves,and Log-rank test was used to compare whether the survival curve was statistically different.The effects of chemotherapy and PD-L1expression on the prognosis of different molecular types were analyzed.Multivariate Cox regression model was used to analyze the relationship between different molecular subtypes,PD-L1 expression and prognosis of gastric cancer and chemotherapy efficacy,and to calculate risk ratios(HRs)and 95%confidence intervals(95%CI).Results:Among 226 GC patients,the average age was 61.1±10.7 years old,including 172males(76.1%),159 patients(70.4%)with TNM stage III.The positive rates of MLH1,MSH2,MSH6 and PMS2 were 85.8%,96.0%,86.7%and 85.8%,respectively.The results showed that the sensitivity and specificity of IHC method were 88.0%and90.5%,respectively(Kappa value=0.677).Among the 226 GC patients,54(23.9%)patients were identified as having MSI,13(5.8%)patients were EBV~+,and 93(41.2%)patients were PD-L1-positive.According to molecular subtyping,52(23.2%)patients were defined as the MSI subtype,11(4.9%)patients were defined as the EBV~+subtype,and 161(71.9%)patients were defined as the MSS/EBV~-subtype.Two patients were both positive for MSI and EBV infection.EBV~+cases showed higher PD-L1 positivity than MSI cases and MSS/EBV~-cases(81.8%vs.50.0%vs.35.4%,P=0.003).Compared with the MSI or EBV~+subgroup,GC patients who classified as MSS/EBV~-were associated with the worst outcomes(Log-rank P=0.016).The OS was longer in patients with PD-L1-positive tumors than in those with PD-L1-negative tumors(HR=0.684,95%CI:0.458-1.021,P=0.063).In the subgroup analysis,MSS/EBV~-GCs alone could benefit from postoperative chemotherapy(HR=0.452,95%CI:0.299-0.682,P<0.001),and PD-L1-positive expression could also predict a better prognosis(HR=0.612,95%CI:0.389-0.962,P=0.033).Considering both chemotherapy efficacy and PD-L1 expression in the MSS/EBV~-subgroup,multivariate analysis indicated that chemotherapy could improve the prognosis for PD-L1-negative MSS/EBV~-GCs(HR=0.357,95%CI:0.217-0.587,P<0.001)but not PD-L1-positive MSS/EBV~-GCs.Conclusions:The MSS/EBV~-subtype was associated with the worst prognosis compared to that of the MSI and EBV~+subtypes.The positive expression of PD-L1 is associated with the good prognosis of patients with MSS/EBV~-GC.PD-L1~-/MSS/EBV~-GC can benefit from chemotherapy,however it cannot be considered that PD-L1~+/MSS/EBV~-GC patients can gain survival benefit from chemotherapy.Molecular subtyping combined with PD-L1 expression could serve as a potential strategy to better predict prognosis and guide postoperative chemotherapy of GC patients.