In addition, unlike Pten-null mice that died in utero,43 the Btg3-knockout mice developed normally and were not particularly tumor-prone until 21 months, at which time lung tumors were detected.27 The possibility that the Btg3 deficiency was complemented by the other members of the gene family such as Btg2 has yet to be excluded. The gene discussed is BTG2; the disease is neoplasm.