DFMO treatment leads to the accumulation of the cyclin-dependent kinase inhibitor p27Kip1 protein and causes p27Kip1/Rb-coupled G1 cell cycle arrest in MYCN-amplified NB tumor cells through a process that involves p27Kip1 phosphorylation at residues Ser10 and Thr198. Here, MYCN is linked to neuroblastoma.