PTEN and neoplasm: To investigate tumor susceptibility in the Pten-deficient mice at an adult stage, we generated R26-CreER/+;Ptenfx/fx (referred to as R26-Ptenfx/fx hereafter) and control (R26-Ptenfx/+, Ptenfx/+ or Ptenfx/fx) mice and followed this with 4OHT induced Cre/loxP recombination to excise exon 5 of Pten gene (Figure 2A).