Breast Cancer Risk Factors: Menopausal Hormone Therapy
Menopausal hormone therapy (MHT) is approved by the U.S. Food and Drug Administration (FDA) for the short-term relief of hot flashes and other symptoms of menopause. MHT is also called postmenopausal hormone therapy or hormone replacement therapy (HRT).
The FDA recommends women use the lowest dose of MHT that eases symptoms for the shortest time needed [262]. Women younger than age 60 at the time of starting MHT appear to have more benefits and fewer risk with MHT [270].
While there are different types of MHT (for example, vaginal suppositories and hormone patches), here we discuss oral MHT (pills) and breast cancer risk.
The main types of MHT pills are:
- Estrogen plus progestin
- Estrogen alone
Estrogen alone is linked to an increased risk of uterine cancer. So, it’s only used by women who no longer have a uterus (those who’ve had a hysterectomy).
Women who still have a uterus most often use estrogen plus progestin MHT.
Learn about vaginal MHT and hormone patches.
Estrogen plus progestin menopausal hormone therapy
Estrogen plus progestin menopausal hormone therapy (MHT) can reduce hot flashes and vaginal symptoms related to menopause [262]. However, it should only be taken for the shortest time needed [262]. Before taking estrogen plus progestin MHT, talk with your health care provider about the risks and benefits as well as the length of time to take it. Together, make decisions that are right for you.
Risk of breast cancer
Women who use estrogen plus progestin MHT have an increased risk of breast cancer [262-267].
Within the first year of taking estrogen plus progestin MHT, women have an increased risk of having an abnormal mammogram [268]. Within the first 5 years of use, women have an increased risk of breast cancer [263-264,268].
Every year a woman takes estrogen plus progestin MHT, her risk of breast cancer goes up slightly [265]. Small yearly increases in risk can add up over time.
Some large studies have found women who use estrogen plus progestin MHT for 5 or more years (and are still taking it) about double their breast cancer risk [263-265].
When women stop taking estrogen plus progestin MHT, their risk of breast cancer starts to decline. After about 5-10 years, risk returns to that of a woman who’s never used MHT [263,268-269].
Newer, lower-dose forms of MHT are under study.
Learn about other risk factors for breast cancer.
| For a summary of research studies on MHT and breast cancer risk, visit the Breast Cancer Research Studies section. |
Other health effects
Estrogen plus progestin MHT may have other health risks. Results from the Women’s Health Initiative, a large randomized clinical trial, showed women who took estrogen plus progestin for more than 5 years had more health risks than benefits [270-271].
Although women who used estrogen plus progestin MHT appeared to have a decreased risk of hip (and other bone) fractures and colorectal cancer, those benefits were outweighed by an increased risk of breast cancer and [270-271]:
- Deep vein thrombosis (blood clots in the large veins)
- Pulmonary embolism (blood clots in the lungs)
- Stroke
Study findings also show the use of estrogen plus progestin MHT is linked to an increased risk of other conditions, such as cognitive decline (in women older than 65), urinary incontinence and gallbladder disease [270-272].
Newer, lower-dose forms of MHT are under study.
The table below shows the absolute risks and relative risks of some health conditions with the use of estrogen plus progestin MHT compared to a placebo (an inactive substance sometimes used to have a comparison to a drug in a clinical trial).
Risks of select diseases with use of estrogen plus progestin (E+P) MHT versus placebo | ||||
Disease |
Absolute risk |
Relative risk |
Absolute risk |
Relative risk |
Extra cases seen per 10,000 women ages 50-79 who take E+P for a year: |
Extra cases seen per 10,000 women ages 50-59 who take E+P for a year: |
|||
Breast cancer |
9 extra |
1.2 |
6 extra |
1.2 |
Deep vein thrombosis |
12 extra |
1.9 |
Not available |
Not available |
Probable dementia* |
10 extra |
2.1 |
Not available |
Increased risk |
Pulmonary embolism |
9 extra |
2.0 |
6 extra |
2.1 |
Stroke |
9 extra |
1.4 |
5 extra |
1.5 |
Fewer cases seen per 10,000 women ages 50-79 who take E+P for a year: |
Fewer cases seen per 10,000 women ages 50-59 who take E+P for a year: |
|||
Colorectal cancer |
6 fewer |
0.6 |
1 fewer |
0.8 |
Hip fracture |
6 fewer |
0.7 |
3 fewer |
0.2 |
* In women 65 and older Adapted from Women’s Health Initiative findings [270]. |
||||
Estrogen alone menopausal hormone therapy
Estrogen alone menopausal hormone therapy (MHT) can reduce hot flashes and vaginal symptoms related to menopause [262]. However, it should only be taken for the shortest time needed [262]. Before taking estrogen alone MHT, talk with your health care provider about the risks and benefits as well as the length of time to take it. Together, make decisions that are right for you.
Risk of breast cancer
Some studies suggest women who use estrogen alone MHT have about a 30% increased risk of breast cancer [263-265]. The Nurses’ Health Study, a large cohort study, found women had an increased risk of breast cancer after 5 or more years of taking estrogen alone MHT [274].
However, the Women’s Health Initiative showed women who used estrogen alone MHT had a lower risk of breast cancer than women who got a placebo after an average of 7 years of use [273]. In this study, most women began using estrogen many years after menopause, rather than at the time of menopause. (Usually, women begin taking MHT at the time of menopause.) This may explain some of the differences in findings.
Researchers continue to follow the women in these studies to better understand how estrogen alone MHT affects breast cancer risk.
Learn about other risk factors for breast cancer.
Heart disease benefit – under study
Whether estrogen alone MHT decreases the risk of heart disease is under study [270].
| For a summary of research studies on MHT and breast cancer risk, visit the Breast Cancer Research Studies section. |
Menopausal hormone therapy after a breast cancer diagnosis
Menopausal hormone therapy (MHT) is not usually given to women who’ve had breast cancer because findings from large randomized clinical trials have shown it increases the risk of [275-278]:
- Local breast cancer recurrence
- Metastasis (distant recurrence)
- Cancer in the opposite breast
Learn about other ways to treat menopausal symptoms.
| For a summary of research studies on MHT and breast cancer recurrence, visit the Breast Cancer Research Studies section. |
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1. Know your risk
2. Get screened
* Per National Comprehensive Cancer Network Guidelines 3. Know what is normal for you See a health care provider if you notice any of these breast changes:
To see illustrations of these warning signs, please visit the Warning Signs of Breast Cancer page. 4. Make healthy lifestyle choices
|
Download our Breast Self-Awareness Messages resource for more information.
Updated 12/18/24
This content is regularly reviewed by an expert panel including researchers, practicing clinicians and patient advocates.
