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 [265].

While there are different types of MHT that contain hormones (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.

Learn about vaginal menopausal hormone therapy and hormone patches.

Estrogen plus progestin menopausal hormone therapy

Risk of breast cancer

Women who use estrogen plus progestin menopausal hormone therapy (MHT) have an increased risk of breast cancer [266-271].

Within the first year of taking estrogen plus progestin MHT, women have an increased risk of having an abnormal mammogram [272]. Within the first 5 years of use, women have an increased risk of breast cancer [267-268,272].

Every year a woman takes estrogen plus progestin, her risk of breast cancer goes up slightly [269]. Small yearly increases in risk can add up over time.

Some large studies have found women who use estrogen plus progestin for 5 or more years (and are still taking it) about double their breast cancer risk [267-269].

When women stop taking estrogen plus progestin, 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 [267,272-273].

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 [274].

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 [274]:

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 [274-276].

These findings are based on older forms of estrogen plus progestin MHT. Newer, lower-dose forms of estrogen plus progestin 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 (for women who took E+P compared to women who took a placebo)
	Extra cases seen per 10,000 women who take E+P for a year:
Breast cancer	9 extra	1.2
Deep vein thrombosis	12 extra	1.9
Cognitive decline*	23 extra	2.0
Pulmonary embolism	9 extra	2.0
Stroke	9 extra	1.4
	Fewer cases seen per 10,000 women who take E+P for a year:
Colorectal cancer	6 fewer	0.6
Hip fracture	6 fewer	0.7
* In women 65 and older Adapted from Women’s Health Initiative findings [274].

Estrogen alone menopausal hormone therapy

Risk of breast cancer

Some studies suggest women who use estrogen alone menopausal hormone therapy (MHT) have about a 30% increased risk of breast cancer [267-269].

However, the Women’s Health Initiative showed women who used estrogen alone had a lower risk of breast cancer than women who got a placebo after an average of 7 years of use [277]. 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.) So, the effect on breast cancer risk may vary by when it’s first used.

The results from a large cohort study, where most hormone use started at menopause, raise the question of the safety of longer-term use of estrogen alone. As in the Women’s Health Initiative, the Nurses’ Health Study found no increased risk of breast cancer among women who used estrogen alone for less than 10 years [278]. However, these women had an increased risk of breast cancer after 20 years of use [278].

Researchers continue to follow the women in these studies to better understand how estrogen alone might affect 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 [274].

For a summary of research studies on MHT and breast cancer risk, visit the Breast Cancer Research Studies section.

Recommendations for menopausal hormone therapy

If you’re considering menopausal hormone therapy (estrogen plus progestin or estrogen alone), discuss the risks and benefits with your health care provider.

Menopausal hormone therapy (MHT) is approved by the FDA for the short-term relief of hot flashes and other symptoms of menopause. However, the FDA recommends women use the lowest dose of MHT that eases symptoms for the shortest time needed [265].

MHT after a breast cancer diagnosis

MHT is not usually given to women who’ve had breast cancer because findings from large randomized controlled trials have shown it increases the risk of [279-282]:

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.

1. Know your risk

Talk with both sides of your family to learn about your family health history.
Talk with a health care provider about your risk of breast cancer.

2. Get screened

Talk with a health care provider about which screening tests are right for you if you’re at higher risk.
Have a mammogram every year starting at age 40 if you’re at average risk.*
Have a clinical breast exam at least every 3 years starting at age 25, and every year starting at age 40.*

* Per NCCN Guidelines

3. Know what is normal for you

See a health care provider if you notice any of these breast changes:

Lump, hard knot or thickening inside the breast or underarm area
Swelling, warmth, redness or darkening of the breast
Change in the size or shape of the breast
Dimpling or puckering of the skin
Itchy, scaly sore or rash on the nipple
Pulling in of the nipple or other parts of the breast
Nipple discharge that starts suddenly
New pain in one spot that doesn’t go away

To see illustrations of these warning signs, please visit the Warning Signs of Breast Cancer page.

4. Make healthy lifestyle choices

Maintain a healthy weight.
Make exercise part of your routine.
Limit alcohol intake.
Limit menopausal hormone therapy (postmenopausal hormone use).
Breastfeed if you can.

Download our Breast Self-Awareness Messages resource for more information.

Updated 04/25/24

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How Hormones Affect Breast Cancer