2.3. Critical miRNA-Target Gene Pairs Screening and Correlation Analysis

To identify critical miRNA-target gene pairs affecting tumorigenesis, we combined DEGs, DEMs and two experimentally validated miRNA-target gene databases, miRTarBase and miRecords. miRNA-target gene pairs were collected from experimentally validated interactions when both miRNA and gene were differentially expressed in tumor tissues. Samples with both miRNAs and mRNAs expression data were obtained and divided into healthy controls, early stage and advanced stage tumors. With the normalized and log2 transformed expression values, Pearson correlation coefficients of miRNA-target gene pairs were calculated for healthy controls. The pairs with Pearson correlation coefficients < -0.2 and corresponding p-value < 0.05 in the healthy controls were considered as tissues-specific pairs. We performed the correlation analysis for these pairs in early stage and advanced stage separately and compared the results with that in healthy controls.