CDX2 is a protein composed of 311 amino acids and is a biomarker for colorectal and rectal cancer. CDX2 is an intestinal-specific transcription factor, with the control site being the colon and the positive site being the nucleus, which regulates the proliferation and differentiation of intestinal epithelial cells, and has a role in maintaining the normal morphology and function of intestinal epithelial cells. CDX2 can be positive in small intestine, colon, appendix mucosal epithelium, pancreas small and medium-sized ductal epithelium, etc. About more than 95% of invasive colorectal and rectal cancer can be detected positive for CDX2, with the higher positive rate in the ileum, and the positive rate of CDX2 decreasing towards the expansion of distal colorectal sites. CDX2, together with CK7, CK20 and Villin, can help to find the primary foci of metastatic cancer, and can be used as an important index for judging the prognosis. Usually, the survival rate of CDX2 positive patients is much higher than that of CDX2 negative patients.