Bilateral Oophorectomy in Relation to Risk of Postmenopausal Breast Cancer: Confounding by Nonmalignant Indications for Surgery?

摘要

Bilateral oophorectomy is often performed during hysterectomy for benign conditions and can reduce breastncancer risk by 20%–50% when performed at younger ages. Accuracy of estimating the decrease in breast cancernrisk associated with bilateral oophorectomy could be affected by common conditions that lead to surgery, suchnas uterine fibroids or endometriosis. The authors examined the potential for confounding by nonmalignantnindications for surgery on breast cancer risk estimates in a population-based case-control study of invasive breastncancer newly diagnosed in 1992–1995. Breast cancer cases (N ¼ 4,935) aged 50–79 years were identifiednfrom Wisconsin, Massachusetts, and New Hampshire tumor registries; similarly aged controls (N ¼ 5,111) werenselected from driver’s license and Medicare lists. Reproductive and medical history was obtained from structuredntelephone interviews. Odds ratios and 95% confidence intervals were estimated with multivariate logistic regres-nsion.Women who underwent bilateral oophorectomy with hysterectomy at age u000140 years had significantly reducednodds of breast cancer (odds ratio ¼ 0.74, 95% confidence interval: 0.60, 0.90) compared with women with intactnovaries and uterus. Effect estimates were virtually unchanged after adjustment for uterine fibroids or endometriosisnhistory. Results indicate that breast cancer risk reductions conferred by bilateral oophorectomy are not stronglynconfounded by failure to account for nonmalignant indications for surgery.