Homozygous recombination of both tumour suppressor genes was confirmed by microdissecting tumours (Fig. 6A,B) and by recombination PCR of floxed p53 alleles (Fig. 6C,D), whereas homozygous recombination of the floxed PTEN alleles was assessed by the expression of pAkt (Fig. 6E,G), which becomes phosphorylated upon loss of function of both copies of PTEN, as described previously (Groszer et al., 2001; Kwon et al., 2001; Marino et al., 2002). Here, PTEN is linked to neoplasm.