CEACAM5 and gastric cancer: For example, piR-823 is the standard biomarker for screening circulating tumor cells (CTCs) in gastric cancer, positively correlates with T stage and distant metastasis, and has a higher positive detection rate compared with that of conventional markers such as serum carcinoembryonic antigen (CEA) and carbohydrate antigen 19–9 (CA19-9) [39].