4.1. Comparison with Cancer Tissue and Corresponding Normal Tissue
Many studies have used microarrays to compare cancer regions with non-cancer regions and detected many cancer-related genes such as oncogenes and tumor suppressor genes [67,68,69]. For example, expression arrays have been successfully used to examine esophageal cancer [70,71], gastric cancer [72,73], colorectal cancer [67], breast cancer [74], and HCC [75,76,77,78], and methylation arrays were used in esophageal cancer [79], gastric cancer [80,81,82], colorectal cancer [83], breast cancer [21,84], and HCC [85,86,87].