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Background Epidemiological evidence supports a positive association between circulating insulin-like growth factor-1 (IGF-1) concentrations and breast cancer risk, but both the magnitude and causality of this relationship are uncertain. We conducted observational analyses with adjustment for regression dilution bias, and Mendelian randomization (MR) analyses to allow causal inference. Patients and methods We investigated the associations between circulating IGF-1 concentrations and incident breast cancer risk in 206,263 women in the UK Biobank. Multivariable hazard ratios (HRs) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models. HRs were corrected for regression dilution using repeat IGF-1 measures available in a subsample of 6,711 women. For the MR analyses, genetic variants associated with circulating IGF-1 and IGFBP-3 levels were identified and their association with breast cancer was examined with two-sample MR methods using genome-wide data from 122,977 cases and 105,974 controls. Results In the UK Biobank, after a median follow-up of 7.1 years, 4,360 incident breast cancer cases occurred. In the multivariable-adjusted models corrected for regression dilution, higher IGF-1 concentrations were associated with a greater risk of breast cancer (HR per 5 nmol/L increment of IGF-1=1.11, 95%CI=1.07-1.16). Similar positive associations were found by follow-up time, menopausal status, body mass index, and other risk factors. In the MR analyses, a 5 nmol/L increment in genetically-predicted IGF-1 concentration was associated with greater breast cancer risk (odds ratio [OR]=1.05, 95%CI=1.01-1.10; Pvalue=0.02), with a similar effect estimate for estrogen positive (ER+) tumors, but no effect found for estrogen negative (ER-) tumors. Genetically-predicted IGFBP-3 concentrations were not associated with breast cancer risk (OR per 1-SD increment=1.00, 95%CI=0.97-1.04; Pvalue=0.98). Conclusion Our results support a probable causal relationship between circulating IGF-1 concentrations and breast cancer, suggesting that interventions targeting the IGF pathway may be beneficial in preventing breast tumorigenesis.


Journal article


Annals of Oncology


Oxford University Press (OUP)

Publication Date