Investigation of MYCN status in neuroblastoma by fluorescence in situ hybridization

Neuroblastoma, a form of neuroblastic tumor, is one of the most common neoplasms seen in early childhood. The diverse clinical behavior of this tumor is most probably explainable by the heterogeneity in the associated genetic changes. We investigated 12 neuroblastoma patients for MYCN amplification and chromosome 2 aneusomy by fluorescence in situ hybridization (FISH) and results were correlated with conventional cytogenetics. Samples from both primary tumor tissue and bone marrow metastasis were available in two cases. The copy number of MYCN oncogene paralleled that of chromosome 2 in 10 cases, whereas two cases (16.7%) showed numerous distinct signals within the nuclei of the tumor cells, consistent with MYCN amplification as double minute (dmin). The morphology of dmin in one case was of an extremely small type and might potentially be missed by conventional chromosome analysis. Discordant cytogenetics and FISH results was observed between primary tumor and metastasis disease in one case, with loss of chromosome 2 tetrasomic and pentasomic cells as well as over-representation of chromosome 2 disomic cells harboring MYCN amplification in bone marrow deposits. Our study reaffirmed the need for MYCN status to be determined in light of chromosome 2 copy number, as recommended by published guidelines. We also showed that genetic heterogeneity might occur between primary tumor and bone marrow metastasis. Finally, atypical dmin morphology when encountered would need confirmation by FISH study.