Indeed, mice carrying genetically modified alleles of the retinoblastoma (Rb) tumor-suppressor gene, causing an increase in the E2F1 activity, showed high predisposition to develop pituitary tumors (10), and this occurs also in mice with impaired function of p27 or p18, both converging on pRB pathway (11, 12). Here, RB1 is linked to pituitary tumor.