RRM2 and gastric cancer: Most have previously been proposed as biomarkers in a specific tumor (or tumor-related condition): C15orf48 in esophageal cancer [51], NF2 in neurofibromatosis [52], CMTM6 in renal adenocarcinoma [53], PLEK2 in lung adenocarcinoma [54], RRM2 in glioma [55], HOXA1 in breast and gastric cancers [56], and SAA2 in renal cancer [57].