IL1RL1 and neoplasm: During intestinal tumorigenesis, IL-33 protein expression is induced in transformed epithelial cells.15,16 We previously reported that IL-33 signaling stimulates the production of pro-tumorigenic IL-6, and that ST2-deficient mice show a delayed tumor growth in the colon.16 Several studies support these findings of a tumor-promoting role of IL-33/ST2 signaling for intestinal tumorigenesis, also using different animal models.15,17 However, the identity of the ST2-expressing cells in CRC lesions and their function during intestinal tumorigenesis is yet to be clearly defined.