Tubal sterilization methods may damage surrounding tissue, potentially disrupting the ovarian blood supply and hormonal functioning, and may decrease breast cancer risk. We examined this hypothesis, within the Nurses' Health Study, among 77,511 women, aged 30-55 years and free of cancer at the start of follow-up in 1976. We documented 4,176 cases of invasive breast cancer from 1976 to 2000. Cox proportional hazards models, adjusting for multiple breast cancer risk factors, provided rate ratios (RR) and 95% confidence intervals (CI). Overall, tubal sterilization was not associated with breast cancer risk (RR=0.95, 95% CI=0.88-1.03). However, tubal sterilizations performed from 1970 to 1974 were inversely associated with risk (RR=0.84, 95% CI=0.73-0.97), while procedures performed in other years were not associated with risk. Among women with procedures performed in 1970-1974, those who were >or=35 years old at the time of sterilization were at the lowest risk (RR=0.81, 95% CI=0.66-0.98), while younger women had a suggested decreased risk (RR=0.87, 95% CI=0.72-1.06). Overall, tubal sterilization was not associated with breast cancer risk. However, a modest inverse association was observed at a time when the potentially destructive unipolar electrocautery method was commonly used, providing some support for an association between lower lifetime exposure to hormones and a decreased risk of breast cancer.
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