Relationship between menopausal symptoms and risk of postmenopausal breast cancer.

BACKGROUND Prior studies indicate that women with menopausal symptoms have lower estrogen levels because they go through menopause as compared with women who do not experience them. Given the central role of hormones in the etiology of breast cancer, a link between menopausal symptoms and breast cancer is plausible. However, no prior studies have evaluated the association between menopausal symptoms and breast cancer risk. METHODS Utilizing data from a population-based case-control study we examined associations between menopausal symptoms and risks of different histologic types of breast cancer among postmenopausal women. We calculated multivariate adjusted odds ratios (OR) using polytomous logistic regression and evaluated several potential effect modifiers. RESULTS Women who ever experienced menopausal symptoms had lower risks of invasive ductal carcinoma [(IDC) OR = 0.5; 95% CI: 0.3-0.7], invasive lobular carcinoma (ILC, OR = 0.5; 95% CI: 0.3-0.8), and invasive ductal-lobular carcinoma (IDLC, OR = 0.7; 95% CI: 0.4-1.2), and these reductions in risk were independent of recency and timing of hormone therapy use, age at menopause, and body mass index. Increasing intensity of hot flushes among women who ever experienced hot flushes was also associated with decreasing risks of all three breast cancer subtypes (P values for trend all ≤ 0.017). CONCLUSION This is the first study to report that women who ever experienced menopausal symptoms have a substantially reduced risk of breast cancer, and that severity of hot flushes is also inversely associated with risk. IMPACT If confirmed, these findings could enhance our understanding of breast cancer etiology and factors potentially relevant to prevention.