The expression of MDSC marker genes such as Itgam, S100a9, and Clec4e, and tumor proliferation-associated genes, Ccnd1 (Cyclin D1) and Myc (c-Myc), was enhanced after PGE2-administration (Fig. 5d), indicating that MDSC expansion and tumor growth are promoted by PGE2. This evidence concerns the gene S100A9 and neoplasm.