| Background and Objective:Gastric carcinoma is one of the most common digestive system tumors around the world,ranking third in tumor-related deaths,especially in East Asia,the incidence and mortality of GC are higher.With the rapid development of diagnostic techniques,surgical treatments,radiotherapy and chemotherapy,and targeted therapy,the survival rate of early GC patients has been greatly improved,but the survival and prognosis of patients with advanced GC are still poor.The pathogenesis of gastric cancer involves Helicobacter pylori(HP)infection,chronic active or atrophic gastritis and intestinal metaplasia,etc.From the perspective of molecular pathology,gastric cancer is a chronic proliferative disease and it is characterized by a variety of genetic and epigenetic abnormal changes,that is,a disease with abnormal gene expression.Recent studies have shown that microsatellite instability(MSI)is closely related to tumorgenesis and is considered to be a new mechanism leads to tumor formation following the activation of proto-oncogenes and the inactivation of tumor suppressor genes.It has been reported that MSI plays an important role in the occurrence of hereditary nonpolyposis colorectal cancer,endometrial cancer,and sporadic gastric cancer.MSI is a type of genomic instability,it mainly result from the dysfunction or abnormality of the DNA mismatch repair(MMR)gene.The main gene members of the MMR system are hMLH1,hMSH2,hPMS2 and hMSH6.Among them,hypermethylation and loss of expression of CpG island of hMLH1 gene is the main mechanism leading to MSI type gastric cancer.In addition,It also plays an important role in the formation of tumors that tumor-associated antigens evade immune surveillance of body,which mainly promote tumor cell proliferation and transfer to distant organs.In recent years,the role of programmed death ligand 1(PD-L1)and its receptor(PD-1)in anti-tumor immunity and immune escape has become a research hotspot.The PD-1 inhibitor Pembrolizumab which is aimed at the PD-L1/PD-1signaling pathway has shown significant clinical efficacy in patients with advanced melanoma and non-small cell lung cancer with high PD-L1 expression.Similarly,on September 22,2017,Pembrolizumab was approved for the treatment of advanced gastric cancer.Anti-PD-1 therapy is a safe and effective option for patients with PD-L1-positive advanced gastric cancer,however,its applicability is inferior to the above tumors.It has been suggested that the expression of defective mismatch repair gene(dMMR),tumor infiltrating lymphocytes(TILs)and PD-L1 can be used as molecular markers for the efficacy of immunosuppressant,but the specific mechanism is not clear,and the relevant research results are still inconsistent.At present,there are few reports on the relationship between MMR functional defects and PD-L1 immune escape in the process of formation of gastric cancer at home and abroad.In this study,the expression of hMLH1,hMSH2 and PD-L1 in gastric cancer tissues was detected by immunohistochemistry.The relationships among the three proteins and clinicopathological features of gastric cancer were analyzed and the mechanism of the development and progression of gastric cancer was further explored,which provide basic research for promoting early diagnosis and treatment of gastric cancer.Material and Methods:100 cases of paraffin-embedded tissues from patients with gastric cancer underwent radical gastrectomy from September 2015 to September 2017,from the Department of Pathology of Kunming Jinyu Laboratory of Yunnan Province,were collected and used as experimental group.All patients were not accepted related chemotherapy or radiotherapy before surgery.Another 50 specimens of paraffin-embedded tissues with non-cancerous gastric mucosa were selected as the control group of this experiment.All the experimental specimens were stained with HE and the expression of hMLH1,hMSH2 and PD-L1 proteins in the specimens were detected by immunohistochemistry.The statistical analysis of the data was performed by SPSS17.0software.Expression of hMLH1 and hMSH2 proteins were expressed as a negative rate,while PD-L1 protein was expressed by positive rate.Among them,the relationship between the expression of hMLH1,hMSH2 and PD-L1proteins and each clinicopathological feature were tested by?~2chi-squcre method,the comparison of various protein expression rates between cancer tissue and non-cancer tissue was performed by Fisher exact probability method,the correlation analysis among the three protein molecules were performed by Spearman test method,all the statistical results were statistically significant with p<0.05(bilateral).Results:1.Immunohistochemical staining results of hMLH1,hMSH2 and PD-L1 protein:1.1 The expression of hMLH1 protein is located in the nucleus and cytoplasm of gastric mucosa and gastric cancer cells and the positive expression is brown.In 50 cases of non-cancerous gastric mucosa,the positive rate was 0%.In 100 cases of gastric cancer,13 cases were negative for hMLH1 protein,and the negative rate was 13%.The negative expression rate of hMLH1 protein was significantly different(p<0.05)compared with non-cancerous gastric mucosa tissues.1.2 The expression of hMSH2 protein is also located in the nucleus and cytoplasm of the cells.The positive expression of the nucleus is brown and the cytoplasm is stained in small amounts.In 50 cases of non-gastric cancer tissues,the positive rate was also positive,the negative rate was 0%;in 100 cases of gastric cancer tissue,hMSH2 protein was negatively expressed in 17 cases,the negative rate was 17%.Compared with non-cancerous gastric mucosa tissues,hMSH2 protein negative expression was a significant difference in the negative rate(p<0.05).1.3 The expression of hMLH1 and hMSH2 protein in gastric cancer tissues were decreased.In 100 cases of gastric cancer tissues,the negative expression of hMLH1 or hMSH2 protein were 30 cases(30%)and 0 cases of negative expression of both proteins at the same time.For a protein deletion,the negative expression rate of hMLH1protein was 13%,and the negative expression rate of hMSH2 protein was 17%,the difference between the two groups was not statistically significant(P>0.05).1.4 The positive expression of PD-L1 is mainly located on the cell membrane of gastric cancer cells and cancerous interstitial lymphocytes,and the cytoplasm also has a lighter coloration.PD-L1 were negatively expressed in 50 cases of non-cancerous gastric mucosa,0 cases were positive,and the positive rate was 0%.In 100 cases of gastric cancer,61 cases were positive and 39 cases were negative,positive rate was 61%.Compared with non-cancerous gastric mucosa,the positive expression of PD-L1 was significantly different(p<0.05).2.Association between clinicopathological parameters of patients with carcinama and expression of hMLH1,hMSH2 and PD-L1 protein:2.1 The relationship between the expression of hMLH1 and hMSH2 protein and clinicopathological features in gastric cancer tissues:the relativity between the expression of mismatch repair proteins hMLH1 and hMSH2 and gender,age,differentiation,tumor size,depth of invasion,lymph node metastasis,vascular tumor thrombus and clinical TNM were no significant(P>0.05).2.2 The association between the positive expression of PD-L1 and clinical pathological features in gastric cancer tissues:The expression of PD-L1 in gastric cancer tissues was closely related to tumor invasion depth,lymph node metastasis,vascular tumor thrombus and TNM staging(p<0.05),regardless of gender,age,differentiation degree and tumor size(p>0.05).3.Correlation between PD-L1 and hMLH1 and hMSH2 protein in gastric cancer:the negative expression of hMSH1 and hMSH2 protein were not obviously correlated with the positive expression of PD-L1 in gastric cancer tissues(p>0.05).Conclusions:1.hMLH1 and hMSH2 proteins were all normally expressed in non-cancerous gastric mucosa tissues and partially expressed in gastric cancer,which suggests that the deletion of hMLH1 and hMSH2 are closely related to the occurrence of gastric carcinama.2.There were no statistically significant difference between deletion of hMLH1 and hMSH2 protein and depth of tumor invasion,lymph node metastasis,vascular tumor thrombus and TNM staging in gastric cancer,suggesting that the loss of both may occur in the early stage of gastric cancer formation instead of advanced phase.The detection of hMLH1 and hMSH2 expression may contribute to the early diagnosis of gastric cancer.3.The expression of PD-L1 in gastric cancer was significantly higher than that in non-cancerous tissues and was closely related to tumor invasion depth,lymph node metastasis,vascular tumor thrombus and TNM staging,indicating that anti-tumor immunity and immune escape mechanism associated with PD-L1 may be involved in the occurrence and development of gastric cancer,further suggesting that the high expression of PD-L1 may be a predictive molecular marker for judging the progression of gastric cancer.4.There are no significant correlation between the expression of hMLH1,hMSH2 and PD-L1 in gastric cancer tissues,suggesting that the mismatch repair genes hMLH1,hMSH2 and immune escapes associated with PD-L1 may be two unrelated pathogens in the development of gastric cancer. |
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