RB1 and neoplasm: While not the primary intention of the study, recent work utilizing an Rb1 allele that could be inactivated and then restored had shown that triple mutant Kras, Trp53, Rb1 (KPR) mice develop aggressive, metastatic LUAD with features of dedifferentiation, which is often not observed in the KP LUAD model until much later in tumor development.135 However, the histologic characterization of these lesions was neither NE nor consistent with SCLC.