SEMIQUANTITATIVE 123I-METAIODOBENZYLGUANIDINE SCORE AS A PROGNOSIS MARKER IN HIGH RISK NEUROBLASTOMA: CORRELATION WITH OTHER PROGNOSTIC MARKERS AND MINIMAL RESIDUAL DISEASE IN BONE MARROW. Purpose: Metaiodobenzylguanidine (MIBG), specifically taken up in cells of sympathetic origin, provides a highly sensitive and specific marker for the detection of metastases in neuroblastoma. Our aim has been to investigate whether response to induction therapy, evaluated by 123I-MIBG correlates with overall survival (OS) and other prognostic factors in children with metastatic neuroblastoma. Patients and Methods: Medical records and imaging studies from 28 patients with stage 4 neuroblastoma have been retrospectively reviewed. Treatment consisted of intensive chemotherapy, delayed surgery, megatherapy and local irradiation. The scintigraphic response was evaluated by 123I-MIBG scans, using a semi-quantitative scoring system for grading positivity (see ref). It was applied as a pilot retrospective study trying to determine the feasibility of this procedure in our setting, in order to be prospectively implemented in the next international cooperative study. Results: Patients whose score at diagnosis was ≤ 14 had better life-expectancy (>90 months) than those with score >14 at diagnosis (p value 0,052). Only 25% of patients with N-Myc amplified neuroblastoma survived more than 20 months compared to 89% of the non-amplified neuroblastoma patients (p value 0,03). A trend correlating abnormal MIBG after induction therapy and worse outcome was observed (survival was 0% if score >0 vs. 35% in the cases with score 0; p value 0.07). Patients with abnormal MIBG after induction were older than those with complete MIBG response (median age at diagnosis: 4.5 vs. 2.8 years respectively; p value 0.14). There were no statistical differences between N-Myc amplification and persistent MIBG uptake after induction (28% vs. 33%; p value 0.79), but there was correlation with time of survival between cases with MIBG after induction >0 and =0 (18.43 vs. 33.45 months respectively; p value 0.059) and Overall Survival between cases with MIBG after induction >0 and =0 (0% vs. 33%; p value 0.063). Conclusions: Semiquantitative 123I-MIBG score post induction therapy can be utilized to identify a subset of ultra-high-risk patients, with worse prognosis, and faster relapses. More studies are needed to obtain a cut point. Nonetheless, alternative therapeutic strategies should be considered for these patients with poor response.