RB1 and primitive neuroectodermal tumor: In a transgenic mouse model of multi-stage pancreatic neuroendocrine carcinogenesis (PNET), RIP-Tag2, expression of the SV-40 T-antigen (Tag) in pancreatic β cells leads to inhibition of the tumor suppressors p53 and Rb, promoting a temporally defined yet stochastic multi-stage pathway to tumorigenesis.