KRAS and colitis: To promote tumor development, we introduced CRC driver mutations; KrasG12D19 or Tgfbr2flox20 or Trp53R270H21 or a combination of the two mutations (Fig. 1a); TP53 and KRAS mutations were observed in colitis-associated tumors8, and loss of the TGFβ type II receptor was shown to be involved in colitis-associated tumor development22.