On the other hand, caution is necessary: CD13 is also present on some tissues of normal adult organisms [85], and the notion that the binding of NGR-peptides is highly specific for a CD13-isoform exclusively overexpressed on tumor vessels [57] has only been shown for the CNGRCG-peptide in NGR-hTNF, but not for GNGRAHA in tTF-NGR. The gene discussed is RTN4R; the disease is neoplasm.