IGF1 and breast cancer: IGF1 was weakly positively associated with breast-cancer risk for premenopausal women (test for trend, p=0·050) and strongly positively associated with breast-cancer risk for postmenopausal women (test for trend p=0·0002; figure 2); the test for heterogeneity by menopausal status at blood collection was not statistically significant (test for heterogeneity p=0·894).