PTEN and neoplasm: We generated mice for primary tumor formation using combinations of conditionally activated tumor-initiating oncogenes (KrasLSL-G12D or R26StopFLP110*) and conditionally deleted tumor suppressor alleles (Smad4flox, Tgfbr2flox, Map3k7flox, PTEN flox, p53flox; an example is shown in Fig. 1a).