The risk of breast cancer in younger women can be influenced by hormone therapy

Monday June 30, 2025

The NIH study could help guide clinical recommendations for the use of hormone therapy in women under the age of 55.

Scientists from the National Institutes of Health (NIH) have found that two current types of hormone therapy can change the risk of breast cancer in women before the age of 55. Researchers have discovered that women treated with hormone therapy of estrogen without opposition (E-HT) were less likely to develop disease than those that did not use hormonal hormone therapy. They also found that women treated with estrogens and progestin hormone therapy (EP-HT) were more likely to develop breast cancer than women who did not use hormone therapy. Together, these results could help guide clinical recommendations for the use of hormone therapy in younger women.

The two hormonal therapies analyzed in the study are often used to manage the symptoms linked to menopause or as a result of hysterectomy (elimination of the uterus) or oophorectomy (elimination of one or two ovaries). Estrogen therapy without opposition is only recommended for women who have had a hysterectomy because of its association known with the risk of uterine cancer.

“Hormone therapy can considerably improve the quality of life of women with serious menopause symptoms or those who have undergone surgeries that affect their hormonal level,” said the main author Katie O’Brien, Ph.D., of the National Institute of Environmental Health Sciences (NIEHS). “Our study allows better understanding of the risks associated with different types of hormone therapy, which, we hope, will help patients and their doctors to develop more enlightened treatment plans.”

The researchers carried out a large -scale analysis which included data of more than 459,000 women under the age of 55 in North America, Europe, Asia and Australia. Women who used E-HT had a 14% reduction in the incidence of breast cancer compared to those who have never used hormone therapy. In particular, this protective effect was more pronounced in women who started e-HT at younger ages or used it longer. On the other hand, women using EP-HT have experienced breast cancer 10% higher than non-users, with a rate of 18% higher in women using EP-HT for more than two years compared to those who have never used therapy.

According to the authors, this suggests that for EP-HT users, the cumulative risk of breast cancer before the age of 55 could be around 4.5%, compared to 4.1% risk for women who have never used hormone therapy and a risk of 3.6% for those who used E-HT. In addition, the association between EP-HT and breast cancer was particularly high in women who had not undergone hysterectomy or oophorectomy. This highlights the importance of considering the status of gynecological surgery when assessing the risks of departure hormone therapy, the researchers noted.

“These results underline the need for personalized medical advice when examining hormone therapy,” said the scientist and principal author of Niehs, Dale Sandler, Ph.D. “Women and their health care providers should weigh the advantages of the relief of symptoms compared to the potential risks associated with hormone therapy, in particular EP-HT. For women with an intact uterus and ovaries, the increased risk of breast cancer with EP-HT should cause careful deliberation. ”

The authors noted that their study is consistent with major previous studies that document similar associations between hormone and the risk of breast cancer in older and postmenopausal women. This new study extends these results to younger women, providing essential evidence to help guide decision -making for women as you go.

About the National Institute of Environmental Health Sciences (NIEHS): Niehs supports research to understand the effects of the environment on human health and is one of the national institutes of health. For more information on NIEHS or environmental health subjects, visit www.niehs.nih.gov or subscribe to a list of news.

On the National Institutes of Health (NIH): The NIH, the country’s medical research agency, includes 27 institutes and centers and is a component of the American department of health and social services. NIH is the main federal agency that leads and supports basic, clinical and translational medical research, and studies the causes, treatments and remedies for common and rare diseases. For more information on the NIH and its programs, visit www.nih.gov.

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Reference

O’Brien, K., et al. “Using hormone therapy and breast cancer of young people: a grouped analysis of prospective cohorts included in the collaborative group of premenopausic breast cancer.” Lancet Oncol 2025; 26: 911-23.