Hormone Therapy Type May Alter Breast Cancer Risk for Women Under 55, NIH Finds

Women under 55 who are considering hormone therapy for menopause-related symptoms or surgical recovery may face different risks for breast cancer depending on the type of therapy used, according to new findings from the National Institutes of Health (NIH). A large-scale study suggests that unopposed estrogen therapy may reduce breast cancer risk, while combined estrogen-progestin therapy may raise it—information that could influence future treatment decisions for younger women.

The research analyzed data from more than 459,000 women across four continents. It found that users of unopposed estrogen hormone therapy (E-HT)—typically prescribed to women who have undergone a hysterectomy—had a 14% lower chance of developing breast cancer compared to non-users. This protective effect was even more noticeable in women who began the therapy earlier or used it for longer durations. Conversely, those who used estrogen plus progestin hormone therapy (EP-HT)—commonly given to women with an intact uterus—experienced a 10% higher breast cancer rate than non-users, with that risk climbing to 18% after two years of use.

The study also provided estimates of cumulative risk before age 55: about 3.6% for E-HT users, 4.1% for non-users, and 4.5% for those who used EP-HT. Risks were especially elevated for EP-HT users who had not undergone hysterectomy or oophorectomy, highlighting the importance of accounting for gynecological surgery history when considering hormone therapy. These insights could help clinicians and patients weigh the benefits of symptom relief against cancer risk when evaluating hormone treatment options.

Researchers note that these findings are consistent with earlier studies of postmenopausal women, but offer new insight for younger women considering or already using hormone therapy. The results may prompt more personalized medical discussions between patients and providers as women make decisions about managing menopause symptoms or hormonal changes following surgery.

Article by multiple contributors, based upon information from a press release issued by the National Institutes of Health (NIH)

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