Diverse Links Found Between Hormone Therapy and Early-Onset Breast Cancer

Recent research published in the July issue of The Lancet Oncology reveals that the relationship between hormone therapy and young-onset breast cancer (diagnosed before age 55) is complex and varies depending on the type and duration of hormone use. In a comprehensive study, scientists analyzed data from 10 to 13 prospective cohorts worldwide, involving 459,476 women aged 16 to 54, with 8,455 developing breast cancer before age 55. About 15% of participants reported using hormone therapy, primarily estrogen plus progestin or unopposed estrogen.

Interestingly, women who never used hormone therapy had a 4.1% incidence rate of young-onset breast cancer. The study found no overall increased risk associated with any type of hormone therapy. In fact, there was an inverse association between estrogen-only therapy and breast cancer risk, suggesting a potential protective effect. Long-term use of estrogen alone and use among women without hysterectomy or bilateral oophorectomy showed slight increases in risk, but these findings were not statistically significant.

Moreover, the impact of hormone therapy varied across breast cancer subtypes. Estrogen plus progestin therapy appeared more strongly linked to estrogen receptor-negative and triple-negative cancers, which tend to be more aggressive. The study emphasizes the importance of personalized medical advice when considering hormone therapy, especially for young women.

This research highlights the nuanced and complex relationship between hormone therapy and breast cancer risk, alluding to the need for tailored discussions between patients and healthcare providers. Several authors involved in the study have disclosed ties to the biopharmaceutical industry.

For more detailed information, the full study can be accessed through the DOI: 10.1016/S1470-2045(25)00211-6.

Source: https://medicalxpress.com/news/2025-07-varying-associations-idd-hormone-therapy.html