Retrospective study of peptide receptor radionuclide therapy for Japanese patients with advanced neuroendocrine tumors.

Background Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs is an innovative treatment for advanced somatostatin-positive neuroendocrine tumors (NETs). PRRT cannot be performed in Japan because there is no approval or insurance cover so far. Methods We relied on foreign institutions to perform PRRT for Japanese patients with NETs. We retrospectively evaluated the safety and efficacy of PRRT. The inclusion criteria were pathologically confirmed well-differentiated NET and visible tumor uptake on pre-therapeutic somatostatin receptor scintigraphy. 177 Lu-DOTA-TOC was used as the standard treatment, and patients received three infusions every 8 weeks. Until the end of 2017, combination treatment with 90 Y and 177 Lu-DOTA-TOC was performed using the same protocol. Results Thirty-five patients were evaluated and the primary lesions were pancreas, rectum, small intestine, stomach, and other locations. The partial response rate was 42.9%. Progression-free survival (PFS) was 12.8 months and overall survival was 42.8 months. There was no significant difference in PFS between front-line and late-line PRRT (11.0 months vs. 28.0 months) (p = 0.383). Severe adverse events included lymphocytopenia (20.0%) and thrombocytopenia (5.7%). Myelodysplastic syndrome occurred in one case. Conclusion PRRT was effective and safe for Japanese patients with advanced NETs. PRRT was equally effective as front-line and late-line treatment.