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Hormone Therapy for Breast Cancer
Hormone therapy is recommended for people with hormone receptor-positive breast cancer. You might also hear it called endocrine therapy.
If you have hormone receptor-positive breast cancer, the breast cancer cells have receptors (proteins) that attach to estrogen and/or progesterone. This helps the cancer cells grow. Hormone therapy stops estrogen and progesterone from attaching to these receptors. This type of treatment can reach cancer cells almost anywhere in your body, not just in the breast.
On this page
- When is hormone therapy used for breast cancer?
- How does hormone therapy work?
- Hormone therapy medicines that block estrogen receptors
- Hormone therapy medicines that lower estrogen levels
- Ovarian suppression
- Hormone therapy after surgery for breast cancer
- Less common types of hormone therapy
- More information about hormone therapy
When is hormone therapy used for breast cancer?
- Hormone therapy is recommended for people with hormone receptor-positive breast cancer.
- It does not help people whose tumors are hormone receptor-negative. These tumors do not have receptors that attach to estrogen or progesterone.
Hormone therapy is often used after surgery (as adjuvant therapy) to help reduce the risk of the cancer coming back. Sometimes it starts before surgery, as neoadjuvant therapy.
It is usually taken for at least 5 years.
Treatment longer than 5 years might be offered to people whose cancers have a higher chance of coming back. A test called the Breast Cancer Index might be used to help decide if you will benefit from more than 5 years of hormone therapy.
Hormone therapy can also be used to treat cancer that has come back after treatment or that has spread to other parts of the body.
How does hormone therapy work?
About 2 out of 3 breast cancers are hormone receptor–positive. This means their cells have receptors (proteins) for estrogen, progesterone, or both. These receptors help the cancer cells grow and spread.
If a breast cancer has estrogen receptors, it is known as ER–positive. If it has progesterone receptors, it is known as PR–positive.
Several types of hormone therapy are used for breast cancer. Most types either lower estrogen levels in the body or stop estrogen from helping breast cancer cells grow.
Hormone therapy medicines that block estrogen receptors
These medicines work by stopping estrogen from fueling breast cancer cells to grow.
Selective estrogen receptor modulators (SERMs)
SERMs work by blocking estrogen from attaching to cancer cells. This stops the signal that tells the cancer cells to grow and divide. They have anti-estrogen effects in breast tissue but act more like estrogen in other parts of the body, such as the uterus and bones.
These medicines are pills, taken by mouth.
Tamoxifen can be used to treat women with breast cancer, before or after menopause.
It can be used to:
- Lower the risk of breast cancer in women who are at high risk but have not yet been diagnosed.
- Treat DCIS. For women who have breast-conserving surgery for hormone receptor–positive ductal carcinoma in situ (DCIS), taking tamoxifen for 5 years lowers the chance of the DCIS coming back. It also lowers the chance of developing a new invasive breast cancer or DCIS in either breast.
- Treat early-stage invasive breast cancer. For women who have surgery for hormone receptor-positive breast cancer, tamoxifen can lower the chances of the cancer coming back, improve survival, and reduce the risk of a new cancer in the other breast. It can be used before or after surgery. When it is used after surgery, it is usually taken for 5 to 10 years. It is used mainly in women who have not yet gone through menopause.
- Treat advanced breast cancer. For women whose hormone receptor-positive breast cancer has spread to other parts of the body, tamoxifen can help slow or stop tumor growth. It may even shrink some tumors.
Possible side effects
The most common side effects of tamoxifen include hot flashes, vaginal discharge, and changes in the menstrual cycle.
A small number of women with cancer that has spread to the bones might have a tumor flare when starting tamoxifen, meaning that the tumor temporarily gets bigger and causes bone pain. This usually goes away quickly.
Less common, serious side effects
These less common but more serious side effects are also possible:
- Uterine cancer: SERMs can increase the risk of endometrial cancer and uterine sarcoma in post-menopausal women. Tell your healthcare team right away if you have any unusual vaginal bleeding. Most uterine bleeding is not cancer, but it always needs to be checked right away.
- Blood clots: Clots most often form in the legs (deep vein thrombosis). These can break loose and block an artery in the lungs (pulmonary embolism). Call your healthcare team right away if you have pain, redness, or swelling in your calf, shortness of breath, or chest pain.
- Stroke: Tamoxifen has also been linked to strokes in post-menopausal women, although this is rare. Tell your healthcare team right away if you have severe headaches, confusion, or trouble speaking or moving.
- Eye problems: Cataracts can sometimes develop while taking tamoxifen. Tell your healthcare team right away if you notice any changes in your vision.
- Bone effects: Tamoxifen affects bones differently depending on whether you’ve gone through menopause. In pre-menopausal women, it can cause some bone thinning. In post-menopausal women, it may actually strengthen bones.
For most women with hormone receptor-positive breast cancer, the benefits of these medicines far outweigh the risks.
Selective estrogen receptor degraders (SERDs)
Like SERMs, these medicines attach to estrogen receptors. But SERDs bind to the receptors more tightly and cause them to break down. These medicines have anti-estrogen effects throughout the body.
SERDs are used most often in women who are past menopause. When given to pre-menopausal women, they need to be combined with a luteinizing hormone-releasing hormone (LHRH) agonist to stop the ovaries from making estrogen. See Ovarian Suppression.
Fulvestrant can be used:
- Alone to treat advanced breast cancer that has not been treated with other hormone therapy.
- Alone to treat advanced breast cancer after other hormone medicines, like tamoxifen and often an aromatase inhibitor, have stopped working.
- In combination with a CDK 4/6 inhibitor or PI3K inhibitor to treat metastatic breast cancer as initial hormone therapy or after other hormone treatments have been tried.
It is given as 2 injections into the buttocks (bottom). For the first month, the 2 shots are given 2 weeks apart. After that, they are given once a month.
Possible side effects
Common short-term side effects of fulvestrant can include:
- Hot flashes and/or night sweats
- Headache
- Nausea
- Feeling tired
- Loss of appetite
- Muscle, joint, or bone pain
- Injection site pain
Elacestrant (Orserdu) and imlunestrant (Inluriyo) are selective estrogen receptor degraders (SERDs).
Vepdegestrant (Veppanu) works in a similar way but belongs to a newer class of medicines called PROTACs (proteolysis-targeting chimeras). These medicines tag the estrogen receptor so that the cell's own system destroys it.
All three are oral estrogen receptor-targeting medicines that can be used to treat advanced, ER-positive, HER2-negative breast cancer when the cancer cells have an ESR1 gene mutation (change) and the cancer has grown after at least one other type of hormone therapy.
These are taken daily as pills.
Possible side effects
Common short-term side effects of these medicines can include:
- Hot flashes and/or night sweats
- Headache
- Nausea
- Feeling tired
- Loss of appetite
- Muscle, joint, or bone pain
- Increased cholesterol and fat levels in the blood
Hormone therapy medicines that lower estrogen levels
Estrogen stimulates hormone receptor-positive breast cancers to grow. Lowering the level of estrogen in your body can help slow the cancer’s growth or help prevent it from coming back.
Aromatase inhibitors (AIs)
Aromatase inhibitors (AIs) are medicines that stop most estrogen production in the body.
Before menopause, most estrogen is made by your ovaries. If your ovaries are not making estrogen, either because of certain treatments or because you’ve gone through menopause, your body still makes estrogen. It is made in your body fat by an enzyme called aromatase. AIs work by preventing aromatase from making estrogen.
These medicines are useful for women who have gone through menopause. They can also be used in pre-menopausal women when they are combined with ovarian suppression.
These are taken as pills every day to treat breast cancer.
Possible side effects
The most common side effects of AIs include bone, joint, and muscle pain, hot flashes, and vaginal dryness.
Unlike tamoxifen, AIs do not cause uterine cancer and very rarely cause blood clots. However, joint stiffness and pain is common. This can feel like having arthritis in many joints at once. If this becomes a problem, there are a few options:
- Switching to a different AI
- Regular exercise combined with nonsteroidal anti-inflammatory medicines (NSAIDs)
- Taking medications, such as duloxetine (Cymbalta), for the pain
- Using acupuncture for the pain
For some women, the pain is severe enough to stop treatment. If that happens, most doctors recommend switching to tamoxifen to complete the full 5 to 10 years of hormone therapy.
Because AIs significantly lower estrogen levels, they can also cause bone thinning. This may lead to osteoporosis or fractures over time. If you are taking an AI, your healthcare team will likely check your bone density regularly. To help protect your bones, they may prescribe a bisphosphonate, such as zoledronic acid (Zometa) or a RANK ligand, such as denosumab (Prolia).
Ovarian suppression
If you have not yet gone through menopause, your ovaries are the main source of estrogen in your body. Removing them or shutting them down is called ovarian suppression. It puts your body into menopause. This may allow you to use other hormone therapies, such as aromatase inhibitors.
There are several ways to remove or shut down the ovaries to treat breast cancer. All of these methods can cause symptoms of menopause, including hot flashes, night sweats, vaginal dryness, and mood swings.
An oophorectomy is a surgery to remove your ovaries. It is permanent.
These medicines are also called LHRH analogs. They are used more often than oophorectomy. They stop the signal that the body sends to the ovaries to make estrogen. This causes temporary menopause.
Common LHRH medicines include goserelin (Zoladex) and leuprolide (Lupron). They can be used alone or with other hormone medicines (tamoxifen, aromatase inhibitors, fulvestrant) as hormone therapy in pre-menopausal women.
Some chemo medicines can damage the ovaries of pre-menopausal women so they no longer make estrogen. Ovarian function can return months or years later in some women, but in others the damage to the ovaries is permanent and leads to menopause.
Hormone therapy after surgery for breast cancer
After surgery for hormone receptor-positive breast cancer, hormone therapy is given to lower the risk of the cancer coming back.
For women who are post-menopausal when diagnosed with hormone receptor-positive cancer, doctors recommend taking an aromatase inhibitor (AI) at some point during treatment after surgery. Tamoxifen is an option for women who cannot take an AI. Taking it for 10 years is considered more effective than 5 years.
Standard treatment is about 5 years, or tamoxifen and an AI taken in sequence for 5 to 10 years. Women at higher risk of recurrence may be advised to treat for longer than 5 years.
The following schedules are recommended:
- An AI for 5 to 10 years
- An AI for 2 to 3 years, followed by tamoxifen for 2 to 3 years (5 years total)
- Tamoxifen for 2 to 3 years, followed by an AI for 2 to 3 years (5 years total)
- Tamoxifen for 2 to 3 years, followed by an AI for 5 years (7 to 8 years total)
- Tamoxifen for 4½ to 6 years, followed by an AI for 5 years (9½ to 11 years total)
- Tamoxifen for 5 to 10 years
For women who cannot take an AI:
- Tamoxifen for 5 to 10 years is an option.
For women at high risk of recurrence:
- An AI combined with ribociclib (Kisqali) for 3 years, followed by an AI alone to complete 5 years
- An AI combined with abemaciclib (Verzenio) for 2 years, followed by an AI alone to complete 5 years
- Tamoxifen combined with abemaciclib (Verzenio) for 2 years, followed by tamoxifen alone to complete 5 years
If you are pre-menopausal when you are diagnosed with hormone receptor-positive cancer, doctors may recommend starting with tamoxifen and then switching to an aromatase inhibitor (AI) if you go through menopause during treatment.
Another option is ovarian suppression combined with an AI. Pre-menopausal women should not take an AI alone without ovarian suppression, because it can actually raise hormone levels.
The following schedules are recommended:
- Tamoxifen (with or without ovarian suppression) for 5 to 10 years
- Tamoxifen (with or without ovarian suppression) for 5 years, followed by an AI for 5 years if you have gone through menopause by that point
- An AI plus ovarian suppression for 5 to 10 years
For women at high risk of recurrence:
- An AI plus ovarian suppression combined with ribociclib (Kisqali) for 3 years, followed by an AI plus ovarian suppression to complete 5 years
- An AI plus ovarian suppression combined with abemaciclib (Verzenio) for 2 years, followed by an AI alone to complete 5 years
- Tamoxifen combined with abemaciclib (Verzenio) for 2 years, followed by tamoxifen alone to complete 5 years, for women who are not able to take an AI plus ovarian suppression
Less common types of hormone therapy
Some other types of hormone therapy were used more often in the past, but these are rarely given now:
- Megestrol acetate (Megace), a progesterone-like medicine
- Androgens (male hormones) such as testosterone
- Estradiol (a form of estrogen)
These might be an option for people with metastatic disease if other forms of hormone therapy are no longer working, but they can often cause side effects.
More information about hormone therapy
To learn more about how hormone therapy is used to treat cancer, see Hormone Therapy.
To learn about some of the side effects listed here and how to manage them, see Managing Cancer-related Side Effects.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: July 9, 2026
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