A thorough evaluation for metastatic disease is performed before therapy initiation. The following studies are typically performed:
Metaiodobenzylguanidine (mIBG) scan
The extent of metastatic disease is assessed by mIBG scan, which is applicable to all sites of disease (including soft tissue, bone marrow, and cortical bone involvement). Cortical bone metastases are also evaluated by technetium-99 scan. If all sites of bone metastases are imaged by mIBG scan, then subsequent restaging for assessment of disease response may omit the technetium-99 bone scan.[2,3] Approximately 90% of neuroblastomas will be mIBG avid. It has a sensitivity and specificity of 90% to 99% and is equally distributed between primary and metastatic sites. Although iodine 123 (123 I) has a shorter half-life, it is preferred over131 I because of its lower radiation dose, better quality images, less thyroid toxicity, and lower cost.
Imaging with 123 I-mIBG is optimal for identifying soft tissue and bony metastases and was shown to be superior to 18F-fluorodeoxyglucose positron emission tomography–computerized tomography (PET-CT) in one prospective comparison. Baseline mIBG scans performed at diagnosis provide an excellent method for monitoring disease response and performing posttherapy surveillance.
A retrospective analysis of paired mIBG and PET scans in 60 newly diagnosed neuroblastoma patients demonstrated that for International Neuroblastoma Staging System (INSS) stages 1 and 2 patients, PET was superior at determining the extent of primary disease and more sensitive for detection of residual masses. In contrast, for stage 4 disease, 123 I-mIBG imaging was superior for the detection of bone marrow and bony metastases.
Curie score and SIOPEN score
Multiple groups have investigated a semi-quantitative scoring method to evaluate disease extent and prognostic value. The most common scoring methods in use for evaluation of disease extent and response are the Curie and the International Society of Paediatric Oncology European Neuroblastoma Group (SIOPEN) methods.
- Curie score: The Curie score is a semiquantitative scoring system developed to predict the extent and severity of mIBG-avid disease. The use of the Curie scoring system was assessed as a prognostic marker for response and survival with mIBG-avid, stage 4 newly diagnosed high-risk neuroblastoma (N = 280), treated on the Children's Oncology Group (COG) protocol COG-A3973 (NCT00004188). Patients with a Curie score greater than 2 after induction therapy had a significantly worse event-free survival (EFS) than those with scores less than 2 (3-year EFS, 15.4% ± 5.3% for Curie score >2 vs. 44.9% ± 3.9% for Curie score ≤2; P < .001). A postinduction Curie score greater than 2 identified a cohort of patients at greater risk of an event, independent of other known neuroblastoma factors, including age, MYCN status, ploidy, mitosis-karyorrhexis index, and histologic grade.
- SIOPEN score: The SIOPEN independently developed an mIBG scan scoring system that divided the body into 12 segments, rather than nine, and assigned six degrees, rather than four, of mIBG uptake in each segment. A retrospective study of 58 stage 4 patients from the German Pediatric Oncology Group compared the prognostic value of the Curie and SIOPEN scoring methods. At diagnosis, a Curie score of 2 or less and a SIOPEN score of 4 or less (best cutoff) at diagnosis were correlated to significantly better EFS and overall survival, compared with higher scores. After four cycles of induction, those with complete response by mIBG had a better outcome than those with residual uptake, but after six cycles, there was no significant difference.