Single ¹³¹I-MIBG (NET-targeted radiopharmaceutical) + single autologous stem cell rescue shows feasible engraftment but low response in resistant neuroblastoma

¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) is a norepinephrine transporter (NET)-avid targeted radiopharmaceutical for MIBG-avid neuroblastoma; this retrospective expanded-access experience (NCT00107289) at MSK (2008–2020) tested whether one autologous stem cell rescue (ASCR) could “cover” single or tandem MIBG, with/without subsequent chemotherapy, in resistant neuroblastoma (n=96). Hematologic recovery after a single ASCR was generally reliable (neutrophil engraftment 100%; platelet engraftment 90%), but anti-tumor activity was modest. The study defined ORR to include complete, partial, and minor responses: 15% after first MIBG, 21% with tandem MIBG (no meaningful step-up), and 35% when chemotherapy followed single MIBG (61 received post-MIBG chemotherapy overall: 33 after single MIBG and 28 after tandem MIBG). For context, in relapsed/refractory neuroblastoma, response rates with commonly used salvage chemo-immunotherapy regimens such as irinotecan/temozolomide plus anti-GD2 have been reported in the ~40–53% range in COG-era datasets. These are descriptive cross-study benchmarks only: populations, response definitions, and assessment timing differ, and the MIBG study includes minor responses in its ORR.