Prospective Assessment of Patients With Neuroendocrine Tumors and Current or Prior History of Carcinoid Syndrome or Diarrhea Undergoing Peptide Receptor Radionuclide Therapy With or Without Telotristat Ethyl

Inclusion Criteria: * Written informed consent and HIPAA authorization for release of personal health information. NOTE: HIPAA authorization may be included in the informed consent or obtained separately. * Males and females, aged 18 and older * Histologically-confirmed neuroendocrine tumor (GI or other primary) * Presence of somatostatin receptors as by either Ga-68 dotatate imaging or Octreoscan or comparable method, which is a requirement for PRRT (Lutathera ®). Disease does not need to be measurable per RECIST since it is not uncommon to have non-target lesions but not meet criteria for RECIST as long as presence of somatostatin receptors can be demonstrated. NOTE: Patients undergoing other types of PRRT would not be eligible for this clinical trial. * Eligible for treatment with PRRT (Lutathera®) according to institutional practice and product label. * Patient with current or prior history of symptomatic carcinoid syndrome or carcinoid diarrhea as per investigator assessment. Note: prior history and current controlled carcinoid patients are eligible. * Demonstrate adequate organ function as defined in the protocol; all screening labs to be obtained within 28 days prior to registration. * Life expectancy greater than 12 weeks as per investigator opinion * ECOG performance status 0-2 * Women of childbearing potential (WOCBP) must have a negative pregnancy test (urine or serum βhCG) within 7 days prior to study registration. If a urine test is positive or cannot be confirm…