Lethality of atrx loss required the authors to investigate its cancer-promoting properties in highly sensitized tumor-prone mutants, tp53–/–; nf1b–/–; nf1a+/–; atrx+/– and tp53–/–; nf1b–/–; nf1a+/+; atrx+/–. This evidence concerns the gene NFIB and neoplasm.