RB1 and pituitary tumor: Earlier reports describing pituitary tumors because of Rb loss described a similar localization and histology [30], [31], [32], and we tested whether Bmi1 overexpression has an enhanced role on top of Rb loss (GCre;RbLox/Lox;Bmi1LSL n = 12, GCre;RbLox/Lox n = 20).