GRPR and neoplasm: Meanwhile, lower tumor-to-blood ratio of 0.38 ± 0.01 and tumor-to-muscle ratio of 1.59 ± 0.44 were obtained 0.5 h p.i for blocked 64Cu/NOTA-monomer, with 1.49 ± 0.41 and 7.42 ± 0.41 for the unblocking experiments respectively (p < 0.05, Table 2), showing that the tumor localization of 64Cu/NOTA-monomer was a result of the GRPR.