The simian virus 40 big T‐antigen (Tag) oncogene is expressed under the rat insulin promoter (Rip) in these genetically modified mouse models, where it abrogates the Rb and p53 suppressor genes. In this system, the tumor resembles neuroendocrine carcinoma more than well‐differentiated PNENs and grows gradually through hyperplasia, dysplasia, adenoma, and carcinoma. The gene discussed is RB1; the disease is neoplasm.