Superior NET Targeting by Switch From Agonist to Antagonist-mediated Somatostatin Receptor Theranostics Allowing Successful (LM3-based) PRRT of Otherwise Precluded mNET: Intraindividual Proof-of-concept.

We present a case of a 69-year-old woman with metastasized small bowel NET G2 initially treated with somatostatin analogs (SSA). Disease progression was observed under SSA, and poor tracer uptake on [68Ga]Ga-DOTATOC PET/CT precluded peptide receptor radionuclide therapy (PRRT). Subsequently, evaluation with [68Ga]Ga-NODAGA-LM3 PET/CT was performed, which showed markedly better and treatment-sufficient uptake, enabling initiation of PRRT with [177Lu]Lu-DOTA-LM3. After 4 therapy cycles, a positive response was observed. This interesting case nicely demonstrates not only the diagnostic superiority of somatostatin receptor antagonist (over agonist) imaging but also the direct translation into successful targeted peptide-mediated radionuclide therapy.