Response rates in metastatic neuroendocrine tumors receiving peptide receptor radionuclide therapy and implications for future treatment strategies

BackgroundPeptide receptor radionuclide therapy is a targeted therapy used to treat unresectable somatostatin receptor-positive neuroendocrine tumors. The objective of this study was to evaluate response rates among neuroendocrine tumors of different primaries and identify factors relevant to future treatment strategies.MethodsWe retrospectively reviewed patients who received peptide receptor radionuclide therapy for neuroendocrine tumors from 2018 to 2019 at our institution. Patients were assessed with computed tomography/magnetic resonance imaging and ⁶⁸Ga-DOTATATE-positron emission tomography before and after 2 or 4 cycles of peptide receptor radionuclide therapy. Tumor response was evaluated by RECIST 1.1. Statistics included multinomial logistic regression models and Fisher exact test.ResultsTwenty-seven patients underwent 92 cycles of peptide receptor radionuclide therapy: pancreas (n = 11), small bowel (n = 7), and other (n = 9) neuroendocrine tumors. Overall, 30% (8 of 27) had partial response, 59% (16 of 27) stable disease, and 11% (3 of 27) progressed. Pancreatic neuroendocrine tumors responded differently from small bowel neuroendocrine tumors regardless of cycle number (P = .01). The majority of pancreatic neuroendocrine tumors (6 of 11) had partial response to peptide receptor radionuclide therapy, while all small bowel neuroendocrine tumors had stable disease. Pancreatic neuroendocrine tumors stable after 2 cycles were more likely to respond to additional cycles versus other neuroendocrine tumors (probability: 60% vs 11%).ConclusionPatients with unresectable advanced or metastatic pancreatic neuroendocrine tumors may benefit from a full course of peptide receptor radionuclide therapy, whereas other neuroendocrine tumors appear less likely to respond. Large prospective studies are needed to confirm these findings.