Breast Cancer Risk Factors: Menopausal Hormone Therapy

Menopausal hormone therapy (MHT) is approved by the U.S. Food and Drug Administration (FDA) for the relief of hot flashes and other symptoms of menopause. MHT is also called postmenopausal hormone therapy or hormone replacement therapy (HRT).

It’s recommended women use the lowest dose of MHT that eases symptoms for the shortest time needed [261].

Women who are younger than age 60 when they start MHT appear to have more benefits and fewer risks 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.

Before taking MHT pills, 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.

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 [261]. However, it should only be taken for the shortest time needed [261].

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

Studies show women who use estrogen plus progestin MHT have an increased risk of breast cancer [262-267,658].

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 as a comparison to a drug in a clinical trial).

Risks of select diseases for women who took estrogen plus progestin (E+P) MHT compared to risks for those who took a placebo
Disease	Extra cases seen per 10,000 women who take E+P for a year (Absolute risk)		Relative risk
	Women ages 50-79	Women ages 50-59	Women ages 50-79	Women ages 50-59
Breast cancer	9 extra	6 extra	1.2	1.2
Deep vein thrombosis	12 extra	Not available	1.9	Not available
Probable dementia*	10 extra	Not available	2.1	Increased risk
Pulmonary embolism	9 extra	6 extra	2.0	2.1
Stroke	9 extra	5 extra	1.4	1.5
Disease	Fewer cases seen per 10,000 women who take E+P for a year (Absolute risk)		Relative risk
	Women ages 50-79	Women ages 50-59	Women ages 50-79	Women ages 50-59
Colorectal cancer	6 fewer	1 fewer	0.6	0.8
Hip fracture	6 fewer	3 fewer	0.7	0.2
* In women 65 and older Adapted from Women’s Health Initiative findings, 2024 [270].

 

Estrogen alone menopausal hormone therapy

Estrogen alone menopausal hormone therapy (MHT) can reduce hot flashes and vaginal symptoms related to menopause [261]. However, it should only be taken for the shortest time needed [261].

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) isn’t 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.

Bio-identical hormones

There’s no medical or scientific definition for the term “bio-identical hormones.” So, you may hear this term used in different ways.

Some people use it to describe hormone drugs that have the same chemical and molecular structure as hormones found in the body. (Not all products that claim to be bio-identical meet this definition.)

Compounded bio-identical hormones

“Bio-identical” may also refer to hormone therapies that are custom compounded (when a pharmacist makes a mixture of hormones according to a doctor’s instructions on a prescription) [655-656].

It’s important to remember [655-657]:

• Compounded bio-identical hormones haven’t been shown to be safer than FDA-approved oral MHT. They may even be harmful.
• There’s no evidence compounded bio-identical hormones have fewer health risks than FDA-approved MHT.
• Because they haven’t been well-studied, compounded bio-identical hormones may have more health risks than FDA-approved MHT.
• Compounded bio-identical hormones haven’t been shown to be more effective at treating menopausal symptoms than FDA-approved MHT.
• Compounded bio-identical hormones aren’t more “natural” than FDA-approved MHT.
• There’s no scientific evidence that saliva tests to check hormone levels are useful in making custom compounded hormone therapies.

Learn about ways to treat menopausal symptoms.

SUSAN G. KOMEN®‘S BREAST SELF-AWARENESS MESSAGES

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 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: 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 11/14/25

This content is regularly reviewed by an expert panel including researchers, practicing clinicians and patient advocates.