Based on these results, the authors concluded that the bivalency effect and optimal molecular size of 64Cu-Sar-NGR2 make it a promising PET probe and a potential prototype for developing radiometal-based complexes for tumor diagnosis.60 An interesting study involving 99Tc employed two isomeric hexapeptides containing the NGR sequence—ECG-NGR and NGR-ECG. The gene discussed is RTN4RL2; the disease is neoplasm.