Background: Although reproductive and hormonal factors - such as early menarche and late menopause - have been reported as independent risk factors for cancer, few studies have examined these factors in East Asian populations.
Methods: We performed a large prospective cohort study of 66,466 women. Ovarian hormone exposure was defined as length of time between menarche and menopause. Incidence rates for breast, ovarian, endometrial and cervical cancers were examined separately in relation to reproductive lifespan defined as age at menopause minus age at menarche. Multivariable adjusted hazard ratios (HRs) with 95% confidence intervals (95% CIs) were calculated using the Cox proportional hazards model.
Results: Women with early menarche were at increased risk for developing breast cancer (HR, 1.57, 95% CI, 1.17-2.10) for age at menarche ≤12 years compared to women with age at menarche ≥17 years. Women with late age at menopause (≥52 years) had increased risks for cancers of the breast (HR, 1.59, 95%CI, 1.11-2.28) and ovary (HR, 3.22, 95% CI, 1.09-9.55) compared to women with early menopause (≤45 years of age). Women with longer duration of ovarian hormone exposure (≥40 years) were at increased risk for developing breast cancer (HR, 2.23, 95% CI, 1.35-3.68) as well as endometrial cancer (p for trend, 0.0209).
Conclusions: We showed that longer reproductive spans are associated with an increased risk of breast and endometrial cancer in Korean women.
Keywords: Cancer; Cohort study; Menarche; Menopause.
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