A major international study has revealed new findings about the relationship between hormone replacement therapy (HRT) and breast cancer risk in women under 55.
While HRT is widely used to manage menopause symptoms, researchers from the U.S. National Institute of Environmental Health Sciences set out to understand how it might impact younger women—particularly those who begin therapy after gynecological surgery or during perimenopause.
What the Study Found
Overall, the study found no broad link between HRT use and an increased risk of young-onset breast cancer. However, the type of hormone therapy used made a difference.
Researchers analyzed data from over 459,000 women aged 16 to 54, as part of a large meta-analysis published in The Lancet Oncology. Of these women, 15% reported using hormone therapy, and 8,455 (2%) were diagnosed with breast cancer before the age of 55.
Here’s what stood out:
- Oestrogen-only HRT was linked to a 14% reduced risk of young-onset breast cancer
- Oestrogen plus progestin (combined) HRT was associated with a 10% increased risk — particularly in women who used it for more than two years or who had not undergone surgery to remove their uterus or ovaries.
Why It Matters
Most prior studies focused on postmenopausal women. This research shifts the spotlight to younger women—an often overlooked group—who may begin hormone therapy earlier due to health conditions or surgical interventions.
The researchers noted that the degree of risk or protection varied based on several factors, such as:
- Age when therapy began
- Duration of use
- Whether the woman had undergone gynecological surgery
“Unopposed oestrogen therapy appears to decrease breast cancer risk, while combined oestrogen and progestin therapy increases it,” the authors stated. “These insights can help shape better clinical guidelines for young women considering or using hormone therapy.”
Expert Commentary
Dr. Kotryna Temcinaite, Head of Research Communications at Breast Cancer Now, welcomed the findings as a valuable resource for women under 55:
“This large-scale study offers important insight into how HRT may influence breast cancer risk before menopause. The results are consistent with what we already know—combined HRT carries a slightly higher risk than oestrogen-only HRT. However, for most, the risk is small and is outweighed by the benefits of managing menopausal symptoms.”
Dr. Temcinaite emphasized the importance of personalized care:
“Choosing HRT is a very personal decision. It’s essential that women have clear, evidence-based information, talk openly with their GP or specialist, and feel supported in making the choice that’s best for them.”