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Ovarian removal at or after benign hysterectomy and breast cancer: a nationwide cohort study

Gottschau M1, Kjær SK1,2, Settnes A3, Aalborg GL4, Bens A1, Jensen A1, Munk C1, Mellemkjær L5.

Breast Cancer Res Treat. 2020 Apr 23. doi: 10.1007/s10549-020-05628-z. [Epub ahead of print]

PURPOSE: Large-scale population-based registry studies investigating the risk of breast cancer after removal of both ovaries at hysterectomy for benign conditions in women with no known genetic predisposition to cancer are needed. We aimed to perform such a study taking into account the age at surgery status and use of hormone replacement therapy (HRT).

METHODS: Within the female population of Denmark born 1937-1996, we evaluated breast cancer incidence after unilateral or bilateral oophorectomy concomitant with or after benign hysterectomy in comparison with no surgery and with hysterectomy alone using health registry data during 1978-2016. In a subpopulation followed from 1996, the analyses were stratified according to use of HRT.

 RESULTS: We found a reduced risk of breast cancer among women aged < 45 years at bilateral oophorectomy compared with women with hysterectomy alone (HR = 0.78; 95% CI 0.66, 0.92), whereas slightly increased risks were seen in women above 50 years. In the subpopulation, non-users of HRT aged ≥ 50 years at oophorectomy had a HR of 0.74 (95% CI 0.56, 0.98) for breast cancer after bilateral oophorectomy compared with hysterectomy alone.

CONCLUSIONS: Our large-scale study covering four decades provides evidence that bilateral oophorectomy performed at young age in women with benign indications for hysterectomy is associated with a reduction in breast cancer risk. The finding of a negative association at older ages in women not using HRT deserves further attention.