MYCN and neuroblastoma: For that purpose, we have studied TP53 mutations, MYCN and MDM2 amplification, p14ARF methylation, expression, and homozygous deletions, and have analyzed the effects of chemotherapeutic agents (doxorubicin, etoposide, cisplatin, and melphalan) and of two isomers of retinoic acid (9-cis-RA and all-trans-RA (at-RA)) on the distribution of the cell cycle, the induction of apoptosis, and the expression levels of p53, p21, and Bcl-2 in neuroblastoma cell lines.