RBP4 and neoplasm: Immunohistochemical staining of GFP, RBP4 and PLAC8 showed that bone tumors formed by injection of the mixture of PC3-GFP/PC3-mock or PC3-GFP/PC3-OPG, contained GFP-positive cells and the expression levels of both RBP4 and PLAC8 were increased in tumor cells from PC3-GFP/PC3-OPG-injected mice (Fig. 4B).