Levels of PGE2, which promotes MDSC expansion and tumor development, was reduced in Clec7a−/− mice due to decreased expression of PGE2 synthesizing enzymes, including Ptgs1, Ptgs2, and Ptges3. In addition, the expression of IL-22BP, which can suppress the development of colorectal tumors by inhibiting IL-22, was significantly increased in Clec7a−/− mice. Here, PTGS1 is linked to neoplasm.