NRAS and neuroblastoma: Given that MAPK inhibitors have previously been shown to lack efficacy in ALK-aberrant NB due to activation of a negative feedback loop through PI 3-Kinase, we also examined expression of pAkt in the tumour cells on inhibition of NRAS via a specific siRNA (Supplementary Fig. 18A), and in the PDX tumours shown in Fig. 7E (Supplementary Fig. 18B).