The relationship depends on the type of therapy, duration, and your individual risk factors.
Estrogen-only therapy (for women without a uterus): Re-analyses of WHI data suggest estrogen-only therapy may actually slightly decrease breast cancer risk in some women.
Combined estrogen + progestin therapy: Long-term use (typically beyond 5 years) is associated with a small increase in risk — comparable to lifestyle factors like one glass of wine per day. The absolute risk increase is small, and for most low-risk women, the benefits of hormone therapy outweigh it.
Who should be cautious:
- Women with a personal history of breast cancer — discuss carefully with your clinician and oncologist
- Women with a strong family history — requires individual risk assessment
Good news: Most women who develop breast cancer while taking hormone therapy are diagnosed at an earlier, more treatable stage. Annual mammograms are recommended for all women on hormone therapy.