131I-mIBG therapy in relapsed/refractory neuroblastoma: an old bridge to the future

The prognosis of relapsed/refractory (R/R) neuroblastoma (NB) is still dismal. The role of iodine-131 meta-iodobenzylguanidine (131I-mIBG) treatment as a tool to reduce tumour burden before novel immunotherapies is not defined. Patients with R/R NB were included in a prospective observational study based on two infusions of 131I-mIBG plus melphalan (110 mg/m2), supported by autologous haematopoietic stem cell rescue. The activity of the first administration was 444 MBq (12 mCi/kg), while the second dose was modulated to reach a whole-body absorbed dose of 4 Gy. The International Neuroblastoma Response Criteria (INRC) were used for response. Twenty-six patients with a median age of 5.9 years (range 2.5-17.2 years) were treated. Twenty-three patients presented a bone/bone marrow involvement, and 21 patients presented an uptake at primary site or at soft-tissue sites. The median International Society of Paediatric Oncology Europe Neuroblastoma Group (SIOPEN) skeletal score was 10 (range 1-70). The main recorded toxicities were haematological, with no toxic deaths and only one grade 4 mucositis. Hypothyroidism was reported in 6 patients of the 14 alive patients. The overall response rate was 48% [95% confidence interval (CI) 28% to 69%] with only one progression; after treatment the median SIOPEN skeletal score was 6 (range 0-70) with a median reduction of 35% (range 4.3%-100%). Overall, 52% (95% CI 32% to 73%) of patients achieved/maintained a SIOPEN skeletal score <7 and a soft-tissue lesion <5 cm was seen in 67% (95% CI 43% to 91%). After this treatment, 65% of patients underwent GD2-targeting chimeric antigen receptor (CAR)-T-cell therapy and 50%, high-dose chemotherapy with busulfan and melphalan. The 3-year overall survival was 55% (95% CI 33% to 73%) and event-free survival was 42% (95% CI 23% to 60%). The 131I-mIBG therapy plus melphalan is confirmed to be effective to reduce/control tumour burden. Further studies are needed to clarify the role and timing of this treatment and to integrate its role in the strategy of CAR-T cells.