CEACAM5 and digestive system neoplasm: Moreover, several tumor biomarkers, such as carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), as well as carbohydrate antigen 19 − 9 (CA 19 − 9), are applied in facilitating early diagnosis, reflecting the state of illness, and evaluating postsurgical follow-up of gastrointestinal tumor [14–16].