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Estrogen-Only Hormone Replacement Therapy After Oophorectomy in Women With BRCA1 Mutation Doesn’t Seem to Increase Breast Cancer Risk

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Women with a mutation in the BRCA1 gene have up to a 72% risk of developing breast cancer and up to a 44% risk of developing ovarian cancer. In comparison, women in the general population have about a 1.3% risk of developing ovarian cancer. So, many women with a BRCA1 mutation decide to have their healthy ovaries (and breasts) removed before any cancer is detected. Surgery to remove the ovaries is called oophorectomy. Surgery to remove the healthy ovaries is called protective or prophylactic oophorectomy.

The ovaries are your body’s main source of estrogen. Removing them causes a sudden drop in estrogen levels, putting a woman into immediate menopause, which can bring troubling side effects such as hot flashes, night sweats, and mood swings. To ease these side effects, some women take hormone replacement therapy (HRT) after oophorectomy. But research suggests that some forms of HRT can increase breast cancer risk in women who haven’t been diagnosed. HRT also may increase the risk of recurrence in women who have been diagnosed with the disease. Women who’ve been diagnosed with breast cancer should not take HRT.

A study suggests that using estrogen-only HRT doesn’t increase the risk of breast cancer among women with a BRCA1 mutation who have never been diagnosed and who have preventive oophorectomy.

The research was published in the August 2018 issue of JAMA Oncology. Read the abstract of “Hormone Replacement Therapy After Oophorectomy and Breast Cancer Risk Among BRCA1 Mutation Carriers.”

Slightly less than half the women used HRT

The study included 872 women with a BRCA1 mutation who had never been diagnosed with breast cancer and had preventive oophorectomy. The women were followed for an average of 7.6 years after oophorectomy. The average age of the women in the study was 43.4 years.

Overall, 377 (43%) of the women used HRT after oophorectomy for an average duration of 3.9 years:

  • 259 women (69%) used estrogen-only HRT
  • 66 women (18%) used combination HRT, which includes both estrogen and progesterone
  • 40 women (11%) used progesterone-only HRT
  • 80 women (21%) used another formulation of HRT

During the follow-up time, 92 women (10.6%) were diagnosed with breast cancer.

Overall, there was no real difference in breast cancer rates between women who used HRT and women who didn’t use HRT:

  • 10.3% of women who used HRT were diagnosed with breast cancer
  • 10.7% of women who didn’t use HRT were diagnosed with breast cancer

Estrogen-only HRT seems less risky than combination HRT

Still, 10-year rates of breast cancer were nearly twice as high among women who used combination HRT compared to women who used estrogen-only HRT:

  • 22% of women who used combination HRT were diagnosed with breast cancer
  • 12% of women who used estrogen-only HRT were diagnosed with breast cancer

This difference in breast cancer rates was more notable in women who had oophorectomy before age 45:

  • 24% of these women who used combination HRT were diagnosed with breast cancer
  • 9% of these women who used estrogen-only HRT were diagnosed with breast cancer

The researchers concluded: “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.”

Women must weigh the benefits and risks of using HRT

Still, whether to use HRT or not remains a contentious subject. In 2017, the North American Menopause Society published an updated position statement on using HRT to clarify who might benefit from HRT.

"The use of hormone therapy continues to be one of the most controversial and debated topics," said JoAnn V. Pinkerton, North American Menopause Society executive director. "The goal of this updated version of the Society's position statement is to provide excellent, evidence-based, current clinical recommendations to menopause practitioners for the improvement of care for women depending on them to help relieve menopause symptoms."

Again, it is important to know that if you have been diagnosed with breast cancer, you should not take HRT.

If you're a premenopausal woman with a BRCA1 mutation, you may be considering oophorectomy to reduce your risk of both breast and ovarian cancer. You also may be worried about developing menopausal symptoms after the surgery. Those concerns are understandable, but try not to let them shift your focus from making the best decisions for your health. If you've already had your ovaries removed and are having menopausal symptoms, you may be considering HRT but are worried about the risks.

In either case, you and your doctor should carefully consider both the risks and benefits of using HRT. You also may want to ask your doctor about vaginal or transdermal HRT. Together you can decide if HRT -- or another treatment to ease menopausal side effects -- might be right for you. If you decide to use HRT, use it for the shortest time possible, consider using estrogen-only HRT, and try to make other healthy lifestyle choices that can lower your breast cancer risk. And remember, during and after HRT, make sure to follow the breast cancer screening plan recommended by your doctor for your specific risks and situation.

You can learn more about menopause and ways to manage side effects on the Managing Menopausal Symptoms pages.

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