PROM1 and colorectal cancer: In colorectal cancer, variation in clonogenic potential with specific cell populations have been reported (LaBarge and Bissell, 2008), with CD133+ cells reported to be associated with the CSC population in two separate studies (O'Brien et al., 2007; Ricci-Vitiani et al., 2007), while Shmelkov et al. (2008) reported both CD133+ and CD133- populations were capable of forming colonospheres in vitro and were serially tumorigenic in mice.