In the initial step of this study, we performed immunohistochemical analysis of the SOX2 protein in human gastric cancer tissues, in which the DNA methylation statuses of SOX2 had already been examined [10], and found that a certain number of SOX2 expression-negative cases did not show DNA hypermethylation, leading us to the idea that there is another mechanism underlying SOX2 down-regulation. Here, SOX2 is linked to gastric cancer.