Serum tumour markers, such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9), have often been used in clinical practice, but their utilisation has not been recommended for diagnosis of GC because of the low sensitivity, at <20% for early-stage disease and 20–50% for advanced stage.4 Moreover, concentrations of these tumour markers never increase in early-stage GC, such as stage I. Hence, clinically applicable biomarkers for early detection of GC have been lacking and the discovery of non-invasive biomarkers is anticipated to facilitate a high curability for GC. This evidence concerns the gene CEACAM5 and gastric cancer.