International journal of cancer. Journal international du cancer
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Increased levels of insulin-like growth factor I (IGF-I) may directly stimulate breast cell proliferation and promote growth and survival of transformed cells. Higher levels of IGF-I have been associated with increased risk of premenopausal breast cancer but not postmenopausal breast cancer. We investigated whether circulating levels of IGF-I prior to menopause are associated with breast cancer diagnosed after menopause in a population-based nested case-control study. ⋯ The association between circulating levels of IGF-I and postmenopausal breast cancer risk may be modified by age. Increased levels of circulating IGF-I may be of particular interest in the younger premenopausal women and older postmenopausal women. Age-stratification should be undertaken in larger investigations of IGF-I levels as predictors of postmenopausal breast cancer.