The dose of estrogen in hormone replacement therapy (HRT) has no effect upon breast cancer risk.
Estrogen-alone Therapy and Invasive Breast Cancer Incidence by Dose, Formulation, and Route of Delivery
Authors: Shufelt, C. et. al.
HRT is commonly offered to postmenopausal women. Women who have not had a hysterectomy (surgical removal of the uterus) are offered combined progesterone and estrogen replacement. Women who have had a hysterectomy are considered for estrogen replacement alone. It is understood that women who receive combined HRT are at increased risk for breast cancer compared to women who receive estrogen alone. However, it is unclear if the dose of estrogen in this second group impacts disease risk. This is important because many providers want to prescribe enough estrogen to alleviate menopausal symptoms (vaginal dryness, hot flashes, etc.) while keeping doses low enough to avoid other health complications.
This study evaluated women within the Women’s Health Initiative Observational Study, a project that followed postmenopausal women over time regarding their health issues. Over 26,000 women were evaluated. All of these women had had hysterectomies and were on estrogen HRT. They were categorized as receiving low dose (<0.625 mg) or conventional dose (0.625mg) oral estrogen. Women receiving transdermal doses of estrogen were also followed. The observation period was just over 8 years. The investigators found that the risk of breast cancer was equivalent between the low dose and conventional dose estrogen users. The risk of breast cancer for transdermal estrogen users was lower than that for conventional dose oral users, but the former group was smaller in number and that may explain the difference. This information can be used to counsel women about estrogen HRT and breast cancer risk. There are individual risks and benefits to consider for starting HRT, and the information provided by this study may ease concerns for women and their providers about possible adverse outcomes.