PROM1 and neoplasm: After tumor colonization has been established and the tumor cells have been organized into a solid tumor, other forms of environment stress, including exposure to hypoxia and a cell-adhesion-free environment, promote the switching of CD133− to CD133+ cells, which, because the latter type has been found to have greater stemness and malignancy in colon and other types of cancer [36], [43], may increase later tumor growth.