Many people who have breast cancer use hormonal therapy — also called endocrine therapy — as a part of their treatment plan. There are several types of hormonal therapies. Hormonal therapies are useful for controlling breast cancer cells with certain proteins that make them grow when hormones are present. However, not all breast cancer cells have those proteins, and in those cases, hormonal therapies won’t help.

Hormones and Breast Cancer

Hormones are substances that travel throughout your body in your blood. Their job is to send signals between different parts of the body. Hormones help control body processes such as metabolism, growth, and mood. Certain hormones regulate sexual development and the reproductive system.

Before menopause, the ovaries are the main source of estrogen and progesterone in females. After menopause, the ovaries cease regular function and produce far less estrogen and progesterone. Other tissues, including skin and fat cells, continue to make these hormones at lower levels.

Hormone Receptors

Normal breast cells contain proteins called hormone receptors on their outer surface. There are two main hormone receptors found on these cells: estrogen receptors (ER) and progesterone receptors (PR). These hormone receptor proteins allow a cell to recognize and respond to signals from the hormones estrogen and progesterone.

When breast cells turn cancerous, they often keep their hormone receptors. In some cases, breast cancer cells lose the ability to make ER and PR. When diagnosing someone with breast cancer, doctors often perform tests to determine whether hormone receptors are present. Health care providers may use several terms to describe hormone receptor status:

• Hormone receptor-positive — Breast cancer cells contain ER, PR, or both.
• Hormone receptor-negative — Cells within a breast tumor lack both ER and PR.
• ER-positive — Cells contain ER.
• PR-positive — Cells contain PR.
• Triple-positive — Breast cancer cells contain ER and PR and also make too much of a protein called human epidermal growth factor receptor 2 (usually referred to as HER2).
• Triple-negative — Cells don’t contain either hormone receptor and don’t make much HER2.

Knowing whether breast cancer cells contain ER, PR, or high levels of HER2 helps oncologists (cancer doctors) understand which type of breast cancer you have, predict its course, and plan treatments.

How Does Hormonal Therapy Work?

Hormone receptor-positive breast cancer cells still rely on hormones to grow and survive, even though they have mutated (changed). Hormone treatment blocks natural hormones in the body and disrupts this process. Some types of hormonal therapy attach to hormone receptors on the cell surface, preventing them from interacting with the body’s hormones. Other hormonal therapy drugs cause the body to make less estrogen and progesterone. Either way, hormonal therapy prevents ER-positive or PR-positive breast cancer cells from receiving signals from the body’s hormones.

Hormonal therapy has several purposes. These drugs can prevent cancer cells from growing and dividing. The medications travel throughout the bloodstream, reaching cancer cells that have spread to other places, and can also help prevent relapse (a return of the cancer after treatment).

Hormonal Therapy Differs From Hormone Replacement Therapy

Hormonal therapy drugs that are used to treat breast cancer are different from hormone replacement therapy (HRT). HRT, which is sometimes used to reduce symptoms of menopause, involves taking drugs that contain estrogen or progesterone. HRT is the opposite of breast cancer hormonal therapy, which aims to reduce or block hormones. People may have to quit HRT treatments if they are diagnosed with breast cancer.

When Is Hormonal Therapy Used?

About 2 out of 3 people with breast cancer have hormone receptor-positive cancer cells, according to the American Cancer Society. For this group, hormonal therapy may be an option at different points along the treatment journey:

• Hormonal therapy can help shrink breast tumors before they are surgically removed. This is called neoadjuvant hormonal therapy.
• These medications may be taken for up to 10 years after surgery to prevent the cancer from relapsing. This is called adjuvant therapy.
• Hormonal therapies can treat metastatic breast cancer (cancer that has spread to distant places in the body).
• The U.S. Food and Drug Administration (FDA) has approved hormonal therapy as a risk-reduction strategy. Individuals in specific situations who have a high likelihood of developing breast cancer can take these medications to reduce risk.

People who have hormone receptor-negative breast cancer don’t undergo hormonal therapy. These medications don’t work unless the cancer cells contain estrogen or progesterone receptors.

Types of Hormonal Therapy

There are several hormonal therapy options that fight cancer in different ways. Doctors may recommend different hormonal therapies based on the breast cancer stage (how far cancer has spread within the body) and whether you have gone through menopause. Overall health, bone density, and high risk of developing certain diseases also factor into the decision.

Selective Estrogen Receptor Modulators (SERMs)

Selective estrogen receptor downregulators (SERDs), also known as estrogen receptor downregulators (ERDs), block and degrade estrogen receptors, preventing breast cancer cells from using estrogen to grow.

Tamoxifen is a well-known SERM that blocks estrogen from attaching to estrogen receptors in breast cancer cells. It's often prescribed to premenopausal women with early-stage breast cancer. Tamoxifen is taken as a daily pill for five years or longer.

Other SERMs include:

• Toremifene (Fareston)
• Raloxifene (Evista)
• Fulvestrant (Faslodex)

Aromatase Inhibitors

Aromatase inhibitors (AIs) reduce estrogen production in the body by blocking an enzyme called aromatase. These drugs are most effective for postmenopausal women because their ovaries are no longer producing high levels of estrogen.

Common AIs include:

• Anastrozole (Arimidex)
• Letrozole (Femara)
• Exemestane (Aromasin)

Research has shown that aromatase inhibitors may be taken for five to 10 years after surgery to reduce the risk of breast cancer recurrence.

Even different hormonal drugs of the same class, such as aromatase inhibitors, may have slightly different benefits and risks. Read more about how letrozole and anastrozole compare.

Ovarian Suppression

Surgery or medication can prevent the ovaries from making estrogen. These treatments, often called ovarian ablation or ovarian suppression, trigger menopause in those who are premenopausal. They are often used along with treatments like aromatase inhibitors.

Potential breast cancer treatments that help shut down the ovaries include:

• Oophorectomy (surgery to remove the ovaries)
• Luteinizing hormone-releasing hormone (LHRH) agonist drugs, including leuprolide and goserelin (Zoladex), to temporarily stop estrogen production
• Chemotherapy to halt estrogen production in the ovaries

New Developments in Hormonal Therapy

New types of hormone therapy are being tested in clinical trials, like vepdegestrant, which was given fast-track status by the FDA for treating ER-positive, HER2-negative metastatic breast cancer. This type of breast cancer grows because of the hormone estrogen (ER-positive) but does not have high levels of a protein called HER2 (HER2-negative). It has also spread to other parts of the body (metastatic).

These new treatments block hormone receptors in different ways, giving doctors more options for treating advanced breast cancer.

Side Effects of Hormonal Therapy

Hormonal therapies can cause side effects, especially in premenopausal women or those undergoing ovarian suppression. Common side effects of hormonal therapy include:

• Weight gain
• Hot flashes
• Vaginal dryness
• Mood swings
• Bone and joint pain

Treatments like tamoxifen may also raise the risk of blood clots and uterine cancer, while aromatase inhibitors can lead to bone loss and osteoporosis.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 74,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you tried hormonal therapy to treat breast cancer? Share your experiences in the comments below, or start a conversation by posting on MyBCTeam.