Elevated circulating insulin-like growth factor-1 (IGF-1), a breast epithelial cell mitogen, is associated with breast cancer development. However, its association with breast cancer survival is not established. Circulating concentrations of IGF-1 are controlled via binding proteins, including IGF Binding Protein-3 (IGFBP-3), that may modulate the association of IGF1 with breast-cancer outcomes.
We measured IGF-1 and IGFBP-3 concentrations in serum from 600 women enrolled in the Health, Eating, Activity, and Lifestyle (HEAL) Study, a multiethnic, prospective cohort study of women diagnosed with stage I-IIIA breast cancer. We evaluated the association between IGF-1 and IGFBP-3, and as a ratio, modeled using quintile cut-points, with risk of breast cancer-specific (n=42 deaths) and all-cause mortality (n=87 deaths) using Cox proportional hazards models. In models adjusted for body mass index, ethnicity, tamoxifen use at time of blood draw, treatment received at diagnosis, and IGFBP-3, women in the highest quintile of IGF-1 level had an increased risk of all-cause mortality (Hazard Ratio (HR)=3.10 95% CI 1.21-7.93, p=0.02), although no dose-response association was evident. The IGF-1/IGFBP-3 ratio, an indicator of free IGF-I levels, was significantly associated with increasing risk of all-cause mortality (HR=2.83 95% CI 1.25-6.36 Ptrend=0.01, upper vs. lower quintile) in a fully adjusted model.
In conclusion, high serum levels of IGF-1 and the IGF-1/IGFBP-3 ratio were associated with increased risk of all-cause mortality in women with breast cancer. These results need to be confirmed in larger breast cancer survivor cohorts.