Episomal amplification of MYCN in a case of medulloblastoma.

Gene amplification, in the form of double minutes (dmin) and/or homogeneously staining regions (hsr), is frequently associated with tumor development. A well-known example is neuroblastoma for which MYCN gene (v-myc myelocytomatosis viral-related oncogene) amplification has a relevant prognostic significance. A third cryptic form of amplification, cytogenetically invisible and composed of episomes, has been also described, but it is very rarely seen in primary tumors. In this paper, we report on MYCN amplification, in the form of episomes, in a case of medulloblastoma. Detailed fluorescence in situ hybridization and real-time quantitative polymerase chain reaction analyses revealed an amplified genomic segment of approximately 590 kb containing only the genes MYCN and N-cym (v-myc myelocytomatosis viral-related oncogene, neuroblastoma-derived opposite strand). To the best of our knowledge, this is the first report of a solid primary tumor showing MYCN amplification in the form of episomes.