CEACAM1 and colorectal cancer: Exploring different isoforms of CEACAM1 (CEACAM1-L, CEACAM1-S, cytoplasmic CEACAM1, and membranous CEACAM1) is critical to better understanding the variable role of CEACAM1 in colorectal cancer, gastric cancer, and HCC, and can potentially explain the contrasting results in studies exploring CEACAM1 pathology in the gastrointestinal tract.