MYCN and neuroblastoma: The current major criteria for staging and classification of NB cases are age, tumor histology subtype and differentiation, tumor spreading (about 20% of NB tumors are disseminated at diagnosis, with bone, bone marrow and liver as the more frequent metastatic niches), ploidy status and segmental chromosome aberrations, and MYCN (encoding an oncogenic transcription factor; about 25% of cases) and ALK (encoding an oncogenic receptor tyrosine kinase (RTK); about 3% of cases) genes amplification (MYCN and ALK are physically linked at 2p24-2p23).