Here, we generated Ptend/dSmad4d/dErbb2d/d (CCSPiCrePtend/dSmad4d/dErbb2d/d) mice to examine whether Erbb2 ablation inhibited lung tumor development induced by deletion of Pten and Smad4. In comparison with the wild-type group, all Ptend/dSmad4d/d mice developed lung tumors (adenocarcinomas or, less frequently, adenomas) at 12 to 13 months of age while less than 10% of Ptend/dSmad4d/dErbb2d/d mice had tumor (adenomas) in the lungs at a similar age (Figure 1A–C,G). This evidence concerns the gene PTEN and neoplasm.