Biodistribution studies with the U251 murine model revealed specific MT1-MMP driven uptake of 89Zr-DFO LEM2/15 in GBM tumors (about 30%ID/g at 24h), declining in a time-dependent manner up to 15% ID/g at 7 days p.i. Most likely this increased clearance of radioactivity at tumor site represents metabolism instead of loss of 89Zr, due to lack of complex stability since 89Zr-DFO-LEM2/15 was very stable in serum, with no significant dissociation of the complexes after 7 days. The gene discussed is MMP14; the disease is neoplasm.