By co-injection with an excess of non-labelled peptide, tumour uptake was significantly (p < 0.05) reduced from 13 ± 5% ID/g to 1 ± 0% ID/g for [111In]In-DOTA-PEG2-RM26 and from 7 ± 1% ID/g to 5 ± 1% ID/g for [125I]I-Tyr-PEG2-RM26, indicating specific GRPR-mediated uptake. This evidence concerns the gene GRPR and neoplasm.