Based on the definitive tumour visualisation ensured by high tumour uptake values (2.88 ± 0.64 %ID/g 1 h post-injection), appropriate tumour-to-blood/muscle ratios, and the rapid clearance of 99mTcO-N3S-PEG2-probestin from the circulation (0.60 ± 0.33 %ID/g 1 h post-injection), radiolabelled APN/CD13 specific inhibitors also seem to be precious candidates for the non-invasive identification of receptor expression. This evidence concerns the gene ANPEP and neoplasm.