Patients

This investigation was performed after approval by the Institutional Review Board of G. Gaslini Institute. An aliquot of BM aspirates performed for diagnostic purpose was obtained from six untreated patients (median age 4 years, range 1.5–6 years) with stage 4 disease at diagnosis or relapse [17]. BM samples were obtained upon informed consent from the patients’ legal guardian according to the Helsinki declaration. The proportion of BM infiltrating neuroblasts in these samples ranged from 30 to 70%, as assessed by morphological analysis.