APC and neoplasm: In that study [13], the Muc2/p21 model was generated from mating p21−/− mice with Muc2 knockout mice, in which Muc2 gene plays a critical role in causing tumor formation and β-catenin is inactivated [30]; in the current study, the Apc/p21 mice were generated from mating of p21−/− mice with Apc1638+/− mice, in which Apc mutation plays a causing role on tumor formation because β-catenin is activated [31].