Immature or poorly differentiated neuroblasts have been found to match NB tumor cells of the high-risk group, especially MYCN-amplified NB cells, and to be associated with poor prognosis, while mature or highly differentiated neuroblasts have been shown to match NB cells of the low-risk group and MYCN-nonamplified tumor cells and to be associated with good prognosis [44, 45, 72, 86] (Fig. 6). This evidence concerns the gene MYCN and neuroblastoma.