Many conventional biomarkers, such as the carcinoembryonic antigen (CEA), cancer antigen 19-9 (CA19-9), and cancer antigen 72-4 (CA72-4), are widely utilized in the clinic, but low sensitivities or low specificities reduce the clinical practical value of these markers for the early diagnosis of GC [38–40]. This evidence concerns the gene CEACAM5 and gastric cancer.