As the incidence of cancer is increasing year by year and legumain is highly expressed in cancers, our group designed and synthesized a smart PET tracer 18F-2 to selectively visualize the legumain-positive tumors for cancer diagnosis, but the tumor uptake was not high and nonradioactive probe needed to be co-injected to obtain ideal tumor uptake [24]. This evidence concerns the gene LGMN and neoplasm.