Consistent with a tumour-suppressor role, transgenic mouse models have bring evidence that TGFβ1 is able to protect against mammary tumour development in vivo, because either the suppression of TGFβ1 or the inactivation of the TGFβ signalling pathway results in loss of tumour prohibition and promotes carcinogenesis (Pierce et al, 1995; Bottinger et al, 1997). This evidence concerns the gene TGFB1 and breast cancer.