International journal of cancer. Journal international du cancer
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It is unclear whether age at menarche is causally involved in breast-cancer aetiology, or serves a correlate of other early-life exposures. Other aspects of reproductive life, including cycle length and regularity, climacteric symptoms, reproductive history and oral contraceptive use, are also incompletely investigated. We examined these issues in a population-based case-control study, including 3,016 women aged 50 to 74 years with invasive breast cancer, and 3,263 controls of similar age. ⋯ Lactation, menopausal symptoms or past use of oral contraceptives did not appear associated with breast-cancer risk. Our findings provide some evidence of a role of environmental correlates of early menarche in breast-cancer aetiology, and underline the importance of childbirth, especially early in life, in the prevention of breast cancer. Our data are not readily compatible with an important influence of former oral contraceptive use on post-menopausal breast-cancer risk.