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Type Of Hormone Therapy Can Alter Breast Cancer Risk, Study Says
- July 7, 2025
- Dennis Thompson HealthDay Reporter
Some women have expressed concerns about the risk of breast cancer associated with using hormone therapy to treat symptoms of menopause like hot flashes and night sweats, and now, new research suggests that one type of hormone therapy might increase your risk if you're younger than 55.
Women in this age group who were treated with estrogen plus progestin were more likely to develop breast cancer than those not on hormone therapy, researchers report in The Lancet Oncology.
On the other hand, women younger than 55 given estrogen alone, without progesterone, had a lower risk of breast cancer, results show.
“Hormone therapy can greatly improve the quality of life for women experiencing severe menopausal symptoms or those who have had surgeries that affect their hormone levels,” lead author Katie O’Brien, an epidemiologist with the National Institute of Environmental Health Sciences, said in a news release.
“Our study provides greater understanding of the risks associated with different types of hormone therapy, which we hope will help patients and their doctors develop more informed treatment plans,” she added.
The two hormone therapies analyzed in the study are often used to manage menopause symptoms or to restore hormone levels following surgical removal of the uterus (hysterectomy) or ovaries, researchers said in background notes.
Estrogen therapy without progesterone, also known as unopposed estrogen therapy, is recommended only for women who’ve had a hysterectomy because it’s known to increase risk of uterine cancer, researchers said.
For the study, researchers pooled data from 13 prior studies involving more than 459,000 women younger than 55.
Results showed that women who used unopposed estrogen therapy had a 14% lower risk of breast cancer compared to those not on hormone therapy. Notably, this protective effect was stronger among women who started the treatment at an earlier age or had been on it longer.
Meanwhile, women using estrogen/progestin therapy had a 10% higher risk of breast cancer, with an 18% increased risk found among women who’d been on the treatment for more than two years, researchers report.
Overall, this suggests that the cumulative risk of breast cancer before age 55 for women taking estrogen/progestin is about 4.5%, compared with 4.1% among women who never used hormone therapy and 3.6% for those who used unopposed estrogen therapy, researchers said.
The association between estrogen/progestin therapy and breast cancer was particularly heightened among women who’d not had their uterus or ovaries removed, with around 15% increased risk, researchers noted.
“These findings underscore the need for personalized medical advice when considering hormone therapy,” senior author Dale Sandler, a senior investigator with the NIEHS, said in a news release.
“Women and their health care providers should weigh the benefits of symptom relief against the potential risks associated with hormone therapy, especially estrogen/progestin hormone therapy,” she continued.
“For women with an intact uterus and ovaries, the increased risk of breast cancer with estrogen/progestin hormone therapy should prompt careful deliberation," Sandler said.
Researchers noted their findings are consistent with previous large studies that found similar associations between hormone therapy and breast cancer risk.
More information
The National Council on Aging has more about hormone therapy and breast cancer risk.
SOURCE: National Institutes of Health, news release, June 30, 2025
