The level of RNA m6A modification in the peripheral blood of patients with GC can be used as a marker for GC screening, and the diagnostic value of m6A can be improved by combining it with other tumor markers, such as carcinoembryonic antigen (CEA) or m6A demethylases, such as ALKBH5 and FTO. The gene discussed is CEACAM5; the disease is neoplasm.