Anatomic patterns of relapse and progression following treatment with 131I‐MIBG in relapsed or refractory neuroblastoma

Objectives Patients with metaiodobenzylguanidine (MIBG)‐avid relapsed or refractory neuroblastoma after initial therapy may exhibit transient responses to salvage treatment with iodine‐131 metaiodobenzylguanidine (131I‐MIBG). It is unclear whether disease progression following 131I‐MIBG treatment occurs in previously involved versus new anatomic sites of disease. Understanding this pattern of relapse will inform the use of consolidation therapy following 131I‐MIBG administration. Methods Patients with relapsed or refractory metastatic MIBG‐avid neuroblastoma or ganglioneuroblastoma, who received single‐agent 131I‐MIBG, had stable or responding disease 6–8 weeks following 131I‐MIBG, but subsequently experienced disease progression were included. MIBG scans were reviewed to establish anatomic and temporal evolution of MIBG‐avid disease. Results A total of 84 MIBG‐avid metastatic sites were identified immediately prior to MIBG therapy in a cohort of 12 patients. At first progression, a total of 101 MIBG‐avid sites were identified, of which 69 (68%) overlapped with pre‐treatment disease sites, while 32 (32%) represented anatomically new disease areas. Eight of 12 patients had one or more new MIBG‐avid sites at first progression. Of the 69 involved sites at progression that overlapped with pre‐treatment disease, 11 represented relapsed sites that had cleared following MIBG therapy, two were persistent but increasingly MIBG‐avid, and 56 were stably persistent. Conclusions Previously involved anatomic disease sites predominate at disease progression following 131I‐MIBG treatment. Nevertheless, the majority of patients progressed in at least one new anatomic disease site. This suggests that consolidation focal therapies targeting residual disease sites may be of limited benefit in preventing systemic disease progression following 131I‐MIBG treatment of relapsed or refractory neuroblastoma.