At least two genetic events have been identified which are characteristic of certain neuroblastomas. These are loss of a critical region on the short arm of chromosome 1, and amplification of theMYCNproto‐oncogene. Our studies suggest that the two genetic events may be related, and that loss of heterozygosity (LOH) for chromosome 1p may precede the development of amplification.RASgene mutations appear to be rare, and no other oncogene has been shown to be consistently activated by amplification or other mechanism. LOH for chromosome 14q has been identified recently, but its frequency and significance is not clear. Based on flow cytometric analysis of DNA content, tumour cytogenetics and molecular studies, three distinct genetic subsets of neuroblastomas are emerging. The first is characterized by a hyperdiploid or near‐triploid modal karyotype, with few if any cytogenetic rearrangements. These patients are generally less than one year of age with localized disease and a good prognosis. The second group is characterized by a near‐diploid or near‐tetraploid karyotype, with no consistent rearrangement identified to date. They are generally older patients with more advanced stages of disease that progress slowly and are ultimately fatal. The third group is characterized by a neardiploid or tetraploid karyotype, with deletions or LOH for chromosome 1p, amplification ofMYCN, or both. These patients are generally older with advanced stages of disease which is rapidly progressive. Thus, genetic analysis of neuroblastoma cells by karyotype, flow cytometry and determination ofMYCNcopy number provides information that has prognostic significance and can more appropriately direct the choice of treatment. A better understanding of these genetic abnormalities and the biochemical pathways that they effect may provide insights into malignant transformation and progression, as well as provide targets for future therapeutic app
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