In support of this, studies in neuroblastoma have observed that MYCN functionally cooperates with Twist-1 or BMI-1 to induce neuroblastoma tumorigenesis, where overexpression of Twist-1 or BMI-1 is necessary for tumor growth both in vitro and in vivo (Valsesia-Wittmann et al., 2004; Cui et al., 2007; Huang et al., 2011b). This evidence concerns the gene BMI1 and neuroblastoma.