These results suggest a significant difference in biodistribution characteristics between 89Zr-amatuximab and 89Zr-B3, which may be due to the presence of shed mesothelin in blood and tumor tissue that may affect the serum half-life as well as Ag-specific tumor uptake of radiolabeled amatuximab as previously reported [5]. The gene discussed is MSLN; the disease is neoplasm.