Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors: Agonist, Antagonist and Alternatives.

Peptide receptor radionuclide therapy (PRRT) today is a well-established treatment strategy for patients with neuroendocrine tumors (NET). First performed already more than 30 years ago, PRRT was incorporated only in recent years into the major oncology guidelines, based on its proven efficacy and safety in clinical trials. Following the phase 3 NETTER-1 trial, which led to the final registration of the radiopharmaceutical Luthatera® for G1/G2 NET patients in 2017, the long-term results of the phase 3 NETTER-2 trial may pave the way for a new treatment option also for advanced G2/G3 patients as first-line therapy. The growing knowledge about the synergistic effect of combined therapies could also allow alternative (re)treatment options for NET patients, in order to create a tailored treatment strategy. The evolving thera(g)nostic concept could be applied for the identification of patients who might benefit from different image-guided treatment strategies. In this scenario, the use of dual tracer PET/CT in NET patients, using both [F]F-FDG/[Ga]Ga-DOTA-somatostatin analog (SSA) for diagnosis and follow-up, is under discussion and could also result in a powerful prognostic tool. In addition, alternative strategies based on different metabolic pathways, radioisotopes, or combinations of different medical approaches could be applied. A number of different promising "doors" could thus open in the near future for the treatment of NET patients - and the "key" will be thera(g)nostic!