SAT-163 Status at 10 Years: Long-Term Follow-Up for a Phase 2a Study of High-Specific-Activity (HSA) I 131 Iobenguane in Patients (Pts) with Relapsed/Refractory High-Risk Neuroblastoma

Background: Metaiodobenzylguanidine (MIBG; iobenguane), a guanethidine derivative, is a substrate for norepinephrine reuptake transporter which is highly expressed on the surface of neuroblastoma cells. AZEDRA® (HSA I-131 MIBG) has been approved by the FDA for the treatment of pheochromocytoma and paraganglioma, in pts 12 years and older with MIBG avid, unresectable, locally advanced or metastatic PPGL who require systemic anticancer therapy. The aim of this study was to establish the maximum tolerated dose in children with neuroblastoma, with secondary aims of assessing overall response and tumor and organ dosimetry. Here we report current long-term survival and toxicity data. Methods: Eligible pts were 1-30 years old with resistant neuroblastoma. A diagnostic dose of HSA I-131 MIBG was followed by 3 dosimetry scans to assess radiation dose to critical organs and soft-tissue tumors. To prevent prolonged myelosuppression, autologous hematopoietic stem cells were infused 14 days after therapy. Response and toxicity were evaluated on day 60. Dose-limiting toxicity (DLT) was failure to reconstitute neutrophils to greater than 500/µL within 28 days, or platelets to greater than 20,000/µL within 56 days, or grade 3 or 4 nonhematologic toxicity by Common Terminology Criteria for Adverse Events (version 3.0) except for predefined exclusions. Results: First pt was enrolled in June 2008. 15 pts total were evaluable at 12 (n=5), 15 (n=3), and 18 (n=7) mCi/kg. Mean whole-body radiation was 0.23 mGy/MBq, and mean organ doses were 0.92, 0.82, and 1.2 mGy/MBq of MIBG for the liver, lung, and kidney, respectively. Eight pts had 13 soft-tissue lesions with tumor-absorbed doses of 26-378 Gy. MYC-N amplification was present in two of 11 pts with available results. Of the 15 treated pts, 1 had a complete response, 3 had a partial response, 1 had a mixed response and 6 had stable disease. The remaining 4 had progressive disease. Twelve of the 15 evaluable pts received non-protocol therapy after HSA I-131 MIBG, the remaining 3 died due to tumor without further therapy. At 3.6 years of follow-up the overall survival was 26.7% (95% CI, 8.3%-49.6%). As of March 2018, one remaining pt is in long term follow up with an overall survival of 8.4 years. This pt was previously reported to have a secondary malignancy of myelodysplastic syndrome which has been in remission since receiving an allogenic bone marrow transplant in March 2014. Conclusions: HSA I-131 MIBG contributed to long term median survival of two years and was well tolerated. Treatment showed promising activity in the absence of significant nonhematologic toxicity.