Markedly decreased tumour tracer concentration found upon the administration of the non-labelled blocking NGR peptide further validated the selectivity of this probe for the non-invasive target-specific assessment of APN/CD13 expression (in vivo: blocked vs. unblocked 1.05 ± 0.22%ID/g and 5.42 ± 0.27%ID/g; respectively; and ex vivo: blocked vs. unblocked 0.71 ± 0.13%ID/g and 2.98 ± 0.60%ID/g; respectively). Here, ANPEP is linked to neoplasm.