TP53 and medulloblastoma: However, 100% of triple mutant mice, with Pik3caE545K and heterozygous loss of both Tp53 and activation of Ctnnb1 through in-frame deletion of exon 3, developed WNT-subgroup medulloblastomas by 3 months of age, compared with only 4% of the Blbp-Cre:Ctnnb1+/lox(Ex3):Tp53+/flx controls developing tumours by 11 months [63].