Ultimately, we established a GC gut microbiota prediction model based on gut microbiota data in conjunction with some tumor marker data collected from our clinical GC patients (Table 2), including CEA, CA19-9, AFP, CA12-5, CA15-3, CA72-4, CYFRA 21–1, SCCA, NSE, and ProGRP. This evidence concerns the gene CEACAM5 and gastric cancer.