For all-cause and breast cancer-specific mortality, no heterogeneity of effects was observed by race/ethnicity for IGF1 (P for interaction 0.26 and 0.45, respectively), IGF1R (P for interaction 0.43 and 0.72), or IGFBP2 (P for interaction 0.49 and 0.32). Here, IGF1R is linked to breast cancer.