When tested in vivo in GRPR expressing PC-3 xenografts, both radioantagonists demonstrated high tumor accumulation (6.3 ± 0.5%IA/g and 5 ± 1%IA/g at 1 h pi, respectively), with good retention over time (4 ± 2%IA/g and 3.1 ± 0.1%IA/g at 4 h pi, respectively). The gene discussed is GRPR; the disease is neoplasm.