Hormone replacement therapy (HRT) may not increase the risk of breast cancer among BRCA1-positive women who undergo preventative oophorectomy, according to a study published in JAMA Oncology.1

For this prospective study, researchers evaluated the outcomes of 872 BRCA1carriers without any personal history of cancer who underwent preventative bilateral oophorectomy. Participants completed a questionnaire detailing HRT use at baseline and every 2 years thereafter. 

Of the 872 patients, 495 (57%) women chose not to use HRT therapy; 377 (43%) patients did. Among HRT users, 259 (69%) took estrogen alone, 66 (18%) used estrogen plus progesterone, 40 (11%) used progesterone alone, and 80 (21%) used another formulation. 

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Ninety-two (10.6%) cases of breast cancer were reported during the mean follow-up period of 7.6 years. The use of any HRT post-oophorectomy was not, however, associated with an increase in breast cancer risk (hazard ratio [HR], 0.97; 95% CI, 0.62-1.52; P= .89). 

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Researchers did find that after 10-years, the cumulative incidence of breast cancer was 22% among women who used estrogen plus progesterone vs 12% among patients who used estrogen only (absolute difference, 10%; P= .04). It was suggested that estrogen alone may have a protective effect, decreasing the risk of breast cancer by 8% with every year of use. 

The authors concluded that “these findings suggest that use of estrogen after oophorectomy does not increase the risk of breast cancer among women with a BRCA1 mutation and should reassure BRCA1 mutation carriers considering preventive surgery that HRT is safe. The possible adverse effect of progesterone-containing HRT warrants further study.”


  1. Kotsopoulos J, Gronwald J, Karlan BY, et al. Hormone replacement therapy after oophorectomy and breast cancer risk among BRCA1mutation carriersJAMA Oncol. 2018 Apr 19. doi: 10.1001/jamaoncol.2018.0211 [Epub ahead of print]