Breast cancer is a malignant tumor that begins and grows in the breast. Malignant tumors can grow and invade nearby tissues or travel to distant organs.

This progression is called metastasis. Breast cancer treatment aims to shrink and eradicate tumors as well as prevent future tumor growth.

Hormone therapy, also known as endocrine therapy, can be used to treat some types of breast cancer. It’s commonly combined with other treatments, such as surgery, radiation, or chemotherapy.

Read on as we explore the different types of hormone therapy, when it’s an option, and what you can expect with this treatment.

There are many types of breast cancer. If your cancer tests positive for estrogen receptors (ER) or progesterone receptors (PR), that means it’s using these hormones to grow and potentially spread.

Hormone therapy drugs help block production or stop these hormones from attaching to the hormone receptors (HR). These drugs are used as an active treatment to shrink, control, and eradicate the cancer. They can also lower the chance of recurrence.

About 75 percent of breast cancers are HR-positive.

Some drugs, such as tamoxifen, can be given to people who don’t have breast cancer but have a high risk of developing it. This is commonly called chemoprevention. It may help lower the chances of breast cancer developing in the first place.

Hormone therapy for breast cancer is not the same as hormone replacement therapy (HRT) used for menopause.

Hormone therapy is only effective for HR-positive tumors. If your breast cancer tumor is HR-negative, your oncologist will recommend other treatments.

Hormone therapy can be used in pre- or postmenopausal people with any stage of HR-positive breast cancer.

Hormone therapy that starts before surgery or radiation treatment is called neoadjuvant therapy. This can help shrink the tumor and make surgery easier.

When you begin hormone therapy treatment after surgery or radiation, it’s called adjuvant therapy. The goal here is to lower the risk that cancer will spread or come back.

According to the American Cancer Society, hormone therapy usually lasts at least 5 to 10 years.

Our bodies make a variety of hormones to help control how certain cells work.

Estrogen and progesterone are hormones that are mainly produced in the ovaries of premenopausal women. But they’re also produced in other tissues, so postmenopausal women and men have some estrogen and progesterone, too.

These hormones, however, can promote the growth of some breast cancers.

Treatments like surgery and radiation target specific areas of the body, such as the tumor site or lymph nodes. Because they focus on very specific areas, they’re considered localized treatments.

Hormone therapies, on the other hand, are considered systemic treatments because they target hormones throughout the body.

There are several types of hormone therapy, each with its own mechanism of action. They may help stop or slow growth or prevent recurrence by blocking:

  • ovarian function
  • estrogen production
  • the effects of estrogen

There are several types of hormone therapy to treat breast cancer, including:

Selective estrogen receptor modulators

Also called SERMs, these drugs prevent breast cancer cells from binding to estrogen. SERMs block the effects of estrogen in breast tissue but not in other tissues within the body.

Traditionally, these drugs are usually used in premenopausal women. The most commonly used SERMs include:

  • Tamoxifen (Soltamox). This medication blocks estrogen from binding to estrogen receptors on breast cancer cells. This helps stop the cancer from growing and dividing. People who take tamoxifen for 10 years following breast cancer treatment are less likely to have the cancer return and more likely to live longer than people who took the drug for only 5 years, according to the National Cancer Institute.
  • Fulvestrant (Faslodex). This is an injected ER-blocking medication that’s commonly used to treat advanced breast cancer. Unlike other SERMs, it blocks the effect of estrogen throughout the entire body. Fulvestrant is often used with other drugs such as palbociclib (Ibrance).
  • Toremifene (Fareston). This drug, which isn’t commonly used in the United States, is only approved to treat HR-positive breast cancer in postmenopausal women that’s spread to other parts of the body. It may not be beneficial for people who’ve had limited success using tamoxifen.

Side effects of selective estrogen receptor modulators

Tamoxifen and other SERMs can cause:

These medications may also increase your risk of blood clots and endometrial cancer. But these side effects are rare. In some cases, tamoxifen can cause stroke and may increase your risk of a heart attack.

Aromatase inhibitors

Aromatase inhibitors prevent the production of estrogen from fat tissue but have no effect on the estrogen produced by the ovaries.

Since they can’t stop ovaries from producing estrogen, aromatase inhibitors are only effective in postmenopausal women. They’re approved for postmenopausal women with any stage of ER-positive breast cancer.

Newer research shows that in premenopausal women, an aromatase inhibitor combined with ovarian suppression is more effective than tamoxifen in preventing breast cancer recurrence after initial treatment. It’s now considered the standard of care.

Common aromatase inhibitors include:

Side effects of aromatase inhibitors

Side effects of these medications include:

Estrogen is important for bone development and strength, and aromatase inhibitors can limit natural estrogen production. Taking them may increase your risk of osteoporosis and bone fractures.

Ovarian ablation or suppression

For women who haven’t gone through menopause, ovarian ablation may be an option. This can be done medically (called chemical menopause) or surgically. Either method stops estrogen production, which can help inhibit the growth of cancer.

Surgical ablation is done by removing the ovaries. Without production of estrogen from the ovaries, you will enter permanent menopause.

Symptoms of menopause may include:

  • hot flashes
  • vaginal dryness
  • changes in sex drive

Serious complications after surgical ablation are rare, but you may be more prone to complications if you have diabetes or obesity, or smoke cigarettes.

Luteinizing hormone-releasing hormones

Drugs called luteinizing hormone-releasing hormones (LHRH) can be used to stop the ovaries from producing estrogen altogether. This is known as chemically induced menopause.

These drugs include goserelin (Zoladex) and leuprolide (Lupron).

Ovarian suppression drugs will cause temporary menopause. People who choose this option will usually also take an aromatase inhibitor.

Hormone therapy is quite successful for most people with HR-positive breast cancer. It can also prolong life and reduce cancer-related symptoms in people with metastatic or late-stage HR-positive breast cancer.

A 2017 review of clinical trials found that hormone therapies have significantly decreased cancer-related deaths. Researchers wrote that these therapies have revolutionized breast cancer treatment.

Research from 2019 suggests that the duration of hormone treatment matters a great deal. Study authors found that people who had fewer than 2 years of therapy showed the lowest survival rate.

The overall 5-year survival rate for breast cancer is:

  • localized: 99 percent
  • regional: 86 percent
  • distant: 28 percent

Hormone therapy is an effective treatment for people with HR-positive breast cancer. It works by blocking production or stopping hormones from fueling the breast cancer.

There are several types of hormone therapies. Menopausal status is one factor that will help your doctor determine which therapy is right for you.

Hormone therapy reduces the risk of breast cancer recurrence in women with HR-positive breast cancer. If you have breast cancer, talk with your doctor or oncologist about whether you will benefit from hormone therapy.