IGF1 and breast cancer: There is increasing evidence that the growth hormone-IGF-I axis plays a role in carcinogenesis in the breast (Pollak, 1998; Ruan et al, 1992) and transgenic mice that over-express IGF-I or growth hormone have an increased incidence of mammary cancer (Tornell et al, 1992; Macaulay, 1992; Ruan et al, 1992; Yee, 1998).