In conclusion, the effect of PEGX linker length (x = 2, 3 and 4) in a series of GRPR radioantagonists, ([99mTc]Tc-[N4-PEGx-DPhe6,Leu-NHEt13]BBN(6-13), Figure 1) had little effect on GRPR affinity, binding in GRPR-positive PC-3 cells, metabolic stability in mouse circulation, or PC-3 tumor targeting and overall pharmacokinetics in animal models. This evidence concerns the gene GRPR and neoplasm.