Long-term efficacy and safety of peptide receptor radionuclide therapy in Japanese patients with unresectable neuroendocrine tumor: extension of the Japanese phase I and phase I/II study

Objective Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs is an innovative treatment for advanced well-differentiated neuroendocrine tumors (NETs). In Japan, PRRT with Lutetium-177 oxodotreotide ( 177 Lu- oxodotreotide) was recently approved following Phase I and Phase I/II clinical trials, which primarily assessed safety and response rates. However, its long-term efficacy and safety remain unclear. We conducted a record-based analysis of these trials to evaluate progression-free survival (PFS), overall survival (OS), and long-term safety. Methods We recruited Japanese patients from the Phase I and Phase I/II clinical trials. Patients received four infusions of 7.4 GBq 177 Lu-oxodotreotide every 8 weeks. We reviewed the database records to assess OS, disease progression, and adverse events. Results Twenty-one patients (median age, 57 years) were recruited. The primary tumor sites included the pancreas (n=11), small intestine (n=5), rectum (n=2), lungs (n=2), and stomach (n=1). Twenty (95.2%) patients had liver metastases, whereas 19 (90.5%) had grade 2 tumors. The median PFS period was 36.6 months; median OS period was not reached. Two (9.5%) patients achieved a complete response, 12 (57.1%) achieved a partial response, six (28.6%) had stable disease, and one (4.8%) had progressive disease. One patient had chronic myeloid leukemia 15 months post-PRRT. Conclusions PRRT demonstrated sustained efficacy and safety in Japanese patients with NET.