Stem cell retrograde:A new reason why colorectal cancer is more common than small intestinal cancer?

The intestine is exposed to a dynamic internal environment that is full of phys-iological stimuli and has a high risk of being invaded by pathogenic factors.It has dynamic fold units referred to as crypts that are composed of epithelial cells to ward off potential damage from gut lumen.Apart from the crypt,the small intes-tine(SI)contains villi that is covered by functionally differentiated cells,such as absorptive epithelial cells to maintain nutrient exchange with luminal environ-ments.Intestinal stem cells(ISCs)are responsible for self-repair mechanisms of the intestine epithelium.They have the ability to differentiate and proliferate,are well protected,and are located at the bottom of the intestinal crypt structure(Figure 1A).