Between May 28, 2024, and February 10, 2025, six patients with DLL3 IHC-positive GEP NENs underwent [89Zr]Zr-DFO-SC16.56 immunoPET-CT imaging, which delineated DLL3-avid tumor lesions in five of six patients (two of two GEP NECs, three of four G3 PanNETs). Here, DLL3 is linked to neoplasm.