The Htr2bΔIEC-ER mice were treated with tamoxifen on the 48th day after AOM/DSS treatment and Htr2b gene was ablated at the “late-stage” of CAC, as illustrated in Figure 5A. The 5-HT level in colonic epithelium cells was significantly reduced in Htr2bΔIEC-ER mice (Figure 5B), which is the same as the previous result in Figure 1D. The polyp load of Htr2bΔIEC-ER mouse decreased significantly, but there was no significant difference in polyp multiplicity (Figure 5C). This evidence concerns the gene HTR2B and polyp.