Background: MIBG scans are considered the "gold standard" for detection and staging of neuroblastoma. However, at Memorial Sloan Kettering Cancer Center (MSKCC), over the last decade we have encountered increasing numbers of patients with high-risk neuroblastoma who are long-term progression-free survivors despite having persistently positive MIBG scans after multimodality treatment with chemotherapy, surgery, radiotherapy and anti-GD2 antibody-mediated immunotherapy. We hypothesized that these patients could have mature or inactive disease and that PET scans could assist in identifying this cohort.
Methods: After obtaining permission from MSKCC Institutional Review Board, we retrospectively analyzed records of high-risk stage 4 neuroblastoma patients (>18 months at diagnosis) undergoing concurrent (within 30 days) MIBG and PET scans. We compared progression-free (PFS) and overall survival (OS) in patients with concordant (both MIBG and PET scans positive at ≥1 overlapping site) and discordant (positive MIBG but negative PET scans) using Kaplan-Maier and life table analyses and assessed variables by univariate analysis. "Positivity" was defined as ≥1 site of radio-isotope uptake.
Results: 47 consecutive patients (median age: 3.7±3.1years; 6 with MYCN-amplified disease) were identified between 2006-2013. 24 patients had primary refractory (PR) neuroblastoma and 23 secondary refractory (SR) disease after relapse. 14 patients had concordant and 33 discordant scans. 7 patients (2 with concordant and 5 with discordant scans) had bone marrow (BM) involvement with neuroblastoma at time of scans. The following did not have a significant impact on PFS and OS (p>0.05): MYCN status, paired scans being performed > or <12 months from diagnosis (PR group) or relapse (SR group), post-scan systemic therapy, BM involvement. However, MIBG-PET discordance was associated with significantly better prognosis for PFS (p<0.005; 5 yr PFS 73±8% vs 21±11%) and OS (p=0.06; 3 yr OS 94±4% vs 69±13%).
Conclusion: Negative PET scans after aggressive multimodality therapy for high-risk neuroblastoma might indicate a favorable outcome even if MIBG scans show uptake. Multivariate analysis on a larger cohort of patients is ongoing.