A Screening Of Plasma MiRNAs As Biomakers For Diagnosis Of Gastric Cancer

Gastric cancer is one of the most common maligancies in the world. Although the overall incidence has declined in the recent years, it still remains the fourth most common cancer worldwide and has the second highest mortality rate. The incidence and mortality of gastric cancer are among the top of all kinds of cancers in our country. More than40,000patients are newly diagnosed per year, with two-thirds of which are in advanced stage. Symptoms of gastric cancer in the early stage are slight and not typital. It is usually detected in the advanced stage when the best time for treatment has been missed. The five-year survival rate of early gastric cancer after surgery is more than90%, while that of advanced gastric cancer is only10%-20%relatively. However, only7.5%of the early gastric cancer can be detected. So, early and timely diagnosis is the key to improve the survival rate of gastric cancer.miRNAs are a class of short (20～25nucleotides), noncoding single-stranded RNAs. It is widely accepted that miRNAs can participate in the process of biological regulation of the tumor cells, acting either as oncogenes or tumor suppressor genes. In the recent years, data shows that expression of miRNAs in tissue and cells are stable, with significant tissue specificity and tumor correlation. Looking for appropriate miRNAs as biomarkers of gastric cancer becomes the common orientation of the researchers. Using high-throughput techniques, several miRNAs in gastric cancer tissue have been found. Unfortunately, the tissue samples are difficult to acquire. Detecting miRNAs in tissues is not realistic in clinical diagnosis. On the contrary, peripheral blood samples are easy to get. And miRNAs in peripheral blood are more stable. Like those in tissues, they are also tissue specific and tumor correlated. Several researches have confirmed the existence of miRNAs in blood that were associated with gastric cancer. Throughout the existing researches, they all limited to the single tissue miRNAs screening or the single circulating miRNAs screening, and expression level of miRNAs in tissue and plasma are inconsistent sometimes. If we can find out the miRNAs both differentially expressed in gastric cancer tissue and plasma, and take them as biomarkers for gastric cancer diagnosis, it will have more clinical significance.In this study, we chose5gastric cancer cases matched to those in our previous tissue miRNAs microarray, and5sex and age matched healthy controls, using TaqMan low density array to screen miRNAs in their plasma. Comparing the miRNAs expression profile of plasma and the previous tissue miRNAs microarray result of our research team, those differentially expressed in the both were selected. In the first stage,50pairs of gastric cancer tissues,80gastric cancer plasmas and80cancer-free plasmas matched by age and sex were used to validate the result of the two Microarrays. In the second stage,200gastric cancer plasmas and200cancer-free plasmas matched by age and sex were used to further validate the biomarkers. Receive operating charactreristic curve (ROC) analysis was conducted by SPSS16.0and the area under the ROC curve (AUC) was calculated to evaluate the value of selected miRNAs in diagnosis of gastric cancer. Furthermore, expression level of selected miRNAs was detected in gastric cancer cell lines and their corresponding cell medium.Thirteen miRNAs were found to be differentially expressed in both gastric cancer tissue and plasma, among which8were downregulated and5were upregulated. We selected four miRNAs with at least2of△△Ct in plasma samples (miR-148a, miR-142-3p, miR-26a and miR-195). All of them were downregulated in gastric cancer. In the two validation stages with large samples, the four miRNAs were all significantly downregulated in both the tumor tissues and patients’plasma samples. ROC analysis indicated that miR-26a alone could achieve a good diagnostic efficiency in distinguishing gastric cancer patients and healthy controls with an AUC of0.882(sensitivity=83.6%and specificity=81.5%). Further more, the expression level of miR-26a in plasma did not show any significance with the progression of gastric cancer. Expression level of miR-26a in gastric cancer cell mediums was significantly correlated with that of gastric cancer cells.miR-26a was significantly decreased stably in plasma of gastric cancer patients and could distinguish gastric cancer patients from controls well, with good sensitivity and specificity. It was predicted to be a promising circulating biomarker for early diagnosis of gastric cancer in routine clinical diagnosis.