However, both piR-823 and piR-651 than the commonly used biomarkers such as CA19-9 (carbohydrate antigen 19–9) and CEA (serum carcinoembryonic antigen) for gastric cancer were more sensitive because as a short fragment, piRNAs are not so easily degraded, and levels of piR-651 as well as piR-823 in blood samples are relatively stable and these piRNAs can pass through the cell membrane, and can be detected and isolated easily from body fluids. Here, CEACAM5 is linked to gastric cancer.