IGF1 and breast cancer: The correlations (intra-class or Spearman) between baseline and repeat measures ranged from approximately 0·4 to 0·9 over 1 to 15 years.10, 17, 19, 48, 49, 50 It is therefore likely that the observed association between IGF1 concentrations and breast-cancer risk is an underestimate of the true association, but more reproducibility data are required.