This may be due to the combination ofour initial study, which demonstrated that of the TZDs only Rosi was capable ofinducing PTEN expression, and the fact that natural ligands can be difficult towork with in vitro [21].Despite this, Chen et al. demonstrated that both ciglitazone and 15d-PG-J2 couldupregulate PTEN expression in W-2 thyroid cells [27],which raises the possibility that of the TZDs, Rosi stimulation is limited tobreast cancer. This evidence concerns the gene PTEN and cancer.