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Breast Cancer Research News

Gunter MJ, et al. Insulin, Insulin-Like Growth Factor-I, and Risk of Breast Cancer in Postmenopausal Women. J Natl Cancer Inst. 2008 Dec 30. [Epub ahead of print]

Gunter and colleagues evaluated the fasting serum levels of insulin, glucose, total IGF-I, free IGF-I, insulin-like growth factor binding protein-3, and oestradiol at study entry from 835 incident breast cancer case subjects and from a sub-group of 816 randomly chosen from the Women's Health Initiative Observational Study (WHI-OS): a prospective cohort of 93 676 postmenopausal women. Multivariable Cox proportional hazards models were used to estimate associations between levels of the serologic factors and baseline characteristics and the risk of breast cancer. All statistical tests were two-sided. The authors observed ithat nsulin levels were positively associated with the risk of breast cancer (hazard ratio [HR] for highest vs lowest quartile of insulin level = 1.46, 95% confidence interval [CI] = 1.00 to 2.13, P(trend) = .02); however, the association with insulin level varied by hormone therapy (HT) use (P(interaction) = .01). In a model that controlled for multiple breast cancer risk factors including estradiol, insulin level was associated with breast cancer only among nonusers of HRT (HR for highest vrsus lowest quartile of insulin level = 2.40, 95% CI = 1.30 to 4.41, P(trend) < .001). Obesity (BMI >/=30 kg/m(2)) was also associated with the risk of breast cancer among nonusers of HRT (HR for BMI >/=30 kg/m(2) vs 18.5 to <25 kg/m(2) = 2.12, 95% CI = 1.26 to 3.58, P(trend) = .003). These results suggest that hyperinsulinemia is an independent risk factor for breast cancer and may have a substantial role in explaining the obesity-breast cancer relationship. Leptin is another factor that is thought to be involved in mediating the role of obesity in increasing breast cancer risk.