METTL4 and neoplasm: Immunohistochemistry (IHC) staining of METTL4, 6mA, and HIF-1α showed that the levels of METTL4, 6mA, and HIF-1α were increased in the tumor part, but not in the normal part, of UTUC samples (Fig. 3d, and a representative case was shown in Fig. 3e).