To assess whether the RA target genes identified in vitro were also modulated by RA in vivo, we treated homozygous MYCN transgenic mice with palpable abdominal neuroblastoma with 13-cis-RA (0.72–1.43 mmol 24 h−1) or solvent control, and compared target gene expression by RT–PCR (Figure 1C). This evidence concerns the gene MYCN and neuroblastoma.