INTRODUCTION
Neuroblastoma (NB) is the most common extra-cranial solid tumor in childhood [1] . Its prognosis depends on the stage, age and molecular features on diagnosis.
In cases of high-risk (HR) NB, the chances of cure remain poor, with 3- and 5-year event-free survival rates of 40-50% [2-5] . The current treatment of HR-NB consists of multimodal approaches that include surgical resection of the primary tumor, induction chemotherapy, high-dose myeloablative therapy (HD-MAT) followed by autologous stem cell transplantation (ASCT), radiotherapy, retinoic acid and immunotherapy with chimeric anti-GD2 antibody.
Scintigraphy with 123I-meta-iodobenzylguanidine (123I-MIBG) is recognized to be an effective and reliable method of staging and evaluating the response to treatment of NB patients [6] , while meta-iodobenzylguanidine radiolabeled with iodine-131 (131I-MIBG) has been successfully used as a targeted treatment, administered alone in relapsed/refractory HR-NB or combined with chemotherapy and ASCT[17-24] . This treatment exploits the avidity of NB cells in taking meta-iodobenzylguanidine into the cytoplasm and mitochondria through norepinephrine transporter channels, potentially delivering a lethal radiation dose to the target cells [7-9] .
The main aim of this retrospective study was to analyze the feasibility and toxicity of therapeutic131I-MIBG (Th-131I-MIBG) followed closely by ASCT conditioned with HD-MAT with Busulfan and Melphalan (BuMel) in children affected by HR-NB with residual MIBG-avid disease.
The secondary aim of the study was to evaluate the cumulative risk of progression/relapse (CRR) and the overall survival (OS) and to analyze the association of the principal risk factors with outcome.