WT1 and neoplasm: Of note, although generally the occurrence of ectopic differentiation is considered a characteristic of the WT1-mutant subset of tumours, there are cases known which have mutations in CTNNB1 but not in WT1. Instead they lack expression of WT1 and show a gene expression signature comparable to the WT1-mutant tumours (for instance, tumour set WT-A2 in Corbin et al., 2009).