Somatostatin Analogues vs. Observation After Peptide Receptor Radionuclide Therapy (PRRT) in Nonfunctional Neuroendocrine Neoplasms

Inclusion Criteria: * Histologically or cytologically confirmed metastatic, unresectable, well- or moderately-differentiated, nonfunctional gastrointestinal neuroendocrine tumor (GI-NETs). This includes pancreatic neuroendocrine neoplasms. Any grade (grade 1, grade 2, or grade 3) is permitted. * Measurable disease per RECIST 1.1. * Appropriate for ethanol-stabilized Lu-177 dotatate treatment, as determined by positive screening with SSTR PET/CT and/or currently having received up to 3 fractions of PRRT. (Patients will be randomized prior to the start of PRRT or during PRRT, depending on the timing of enrollment.) * Eligible for somatostatin analogue treatment per the treating physician. * At least 18 years of age. * ECOG performance status ≤ 2 or Karnofsky ≥ 60% * Patients with treated brain metastases are eligible if follow-up brain imaging after central nervous system (CNS)-directed therapy shows no evidence of progression, as determined by a repeat imaging study at least 4 weeks following the completion of treatment. Patients with treated brain metastases must also be off steroids for at least 1 month and stable. * The effects of ethanol-stabilized Lu-177 dotatate and SSAs on the developing human fetus at the recommended therapeutic dose are unknown. For this reason and because radionucleotides and anti-angiogenic agents are known to be teratogenic, people of childbearing potential and people able to father a child must agree to use adequate contraception prior to study entry, for the duration of study participation, and for 4 months following last administration of PRRT for males and 7 months after last administration of PRRT for females, or 4 months after last day of SSA, whichever is later. * Ability to understand and willingness to sign an IRB approved written informed consent document. Legally authorized representatives may sign and give informed consent on behalf of study participants. Exclusion Criteria: * Completed prior treatment with PRRT for non-GI-NET diagnosis (i.e. in need of salvage PRRT treatment). * Major surgery within 4 weeks from randomization to the trial. * Prior or concurrent malignancy whose natural history has the potential to interfere with the safety or efficacy assessment of the investigational regimen. Patients with prior or concurrent malignancy that does NOT meet that definition are eligible for this trial * Currently receiving any investigational agents. * A history of allergic reactions attributed to compounds of similar chemical or biologic composition to SSAs. * Evidence of hypersensitivity to ethanol containing compounds. * Uncontrolled intercurrent illness including, but not limited to: ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, or cardiac arrhythmia. * Pregnant and/or breastfeeding. Women of childbearing potential must have a negative pregnancy test within 15 days of study entry.