Association of near-diploid DNA content and N-myc amplification in neuroblastomas.

Seventeen neuroblastomas at different clinical stages were analysed for their N-myc copy number and flow cytometrically determined DNA content. Aneuploidy was found in 11 patients (65 per cent), whereas the remaining were near-diploid. N-myc amplification was found significantly (P less than 0.05) confined to near-diploid tumors (3 out of 6 cases). This finding indicates a very selective mechanism of oncogene amplification which is independent of gross chromosomal imbalance and limited to specific loci in the human genome. Association of near-diploidy and age at diagnosis older than 24 months was also demonstrated (P less than 0.05). Thus, flow cytometric analysis of DNA content together with N-myc gene dosage allowed us to distinguish two different subsets of neuroblastoma tumors: the first one aneuploid, with single-copy N-myc, usually observed in patients younger than 24 months with localized or IV-S clinical stages; the second one near-diploid, with frequent N-myc amplification, usually observed in patients older than 24 months with advanced clinical stages.