Hormone therapy for breast cancer goes by several names: endocrine therapy, anti-estrogen therapy, hormonal therapy. No matter which name it goes by, this treatment type can be used for all stages of hormone receptor positive breast cancer. We've created a guide to give you an understanding of what you can expect from the therapy.

What is hormone therapy for breast cancer?

Hormones are the body's chemical messengers. Estrogen and progesterone — two hormones produced by the ovaries and certain tissue types, including fat and muscle — control the growth and activity of normal cells in the body.

Both hormones have roles in everything from developing sex characteristics and growing healthy bones to the menstrual cycle and pregnancy. However, these hormones can also fuel the growth of some types of breast cancers.

Breast cancer can develop from various types of cells in the breast. Both normal breast cells and some breast cancer cells have receptors — proteins that can attach to certain substances in blood — that bind to estrogen (ER) or progesterone (PR) and need those hormones to grow.

Breast cancer cells can have receptors sensitive to either estrogen (ER positive or ER+), progesterone (PR positive or PR+) and both hormones (hormone receptor positive or HR+). Or they can have no receptors at all (hormone receptor negative or HR-).

According to the American Cancer Society, about three of every four breast cancers are positive for at least one receptor. All breast cancers are tested for hormone receptor status to help develop an appropriate treatment plan.

Hormone therapy is specifically used for hormone receptor-positive breast cancer.

How does hormone therapy work?

"Hormone therapy can work by blocking hormones from attaching to cancer cell receptors or by hindering the body's production of hormones," says Dr. Preethi Prasad, a breast medical oncologist at Houston Methodist.

There are generally four ways that hormone therapy fights against breast cancer:

• Blocking hormones from attaching to cancer cells
• Preventing the body from producing hormones
• Blocking the effects of hormones
• Lowering the amount of hormones

Is hormone therapy necessary for breast cancer?

"Hormone therapy is essential for breast cancer that is hormone receptor positive," Dr. Prasad explains. "It is not used for breast cancer that is hormone receptor negative."

Hormone therapy can have a variety of uses based on an individual's situation. Breast oncologists may suggest hormone therapy to:

• Prevent breast cancer: For people at higher risk, such as those who carry BRCA1 or BRCA2 gene mutations or have conditions such as ductal carcinoma in situ (DCIS), hormone therapy can help lower their risk of developing HR+ breast cancer
• Primary adjuvant treatment and to prevent recurrence: Hormone therapy may be used along with other treatments after breast surgery to prevent cancer from redeveloping (called recurrence) or spreading to other parts of the body (called metastasis)
• Shrink breast cancer before surgery: If a tumor is large and tests positive for hormone receptors, hormone therapy may be used before surgery
• Stop advanced-stage cancer growth: Hormone therapy may also be used to treat HR+ breast cancer that has spread to another part of the body (metastatic cancer)

What types of hormone therapy exist?

Dr. Prasad says there are four types of hormone therapy used in treating breast cancer: selective estrogen receptor modulators (SERMs), estrogen receptor down regulators (SERDs), aromatase inhibitors and ovarian suppression therapy.

• Aromatase inhibitors: These drugs block the enzyme aromatase, which the body needs to produce estrogen. They are often used in postmenopausal women. Premenopausal women can also use them but must take ovarian function suppressing drugs to see the full effects. Common aromatase inhibitors include anastrozole, exemestane, and letrozole.

• Selective estrogen receptor downregulators (SERDs): These drugs block the actions of estrogen, change the shape of estrogen receptors and reduce the number of available receptors. They are approved only in the metastatic setting. Common SERDs include fulvestrant and elacestrant.

• Selective estrogen receptor modulators (SERMs): These drugs prevent estrogen from binding to cancer cells, blocking the signal that tells the cells to grow and multiply. This can halt cancer growth and may even kill cancer cells. Common SERMs include tamoxifen, raloxifene and toremifene.

• Ovarian suppression therapy: Recommended for premenopausal women with high-risk ER-positive breast cancer, this therapy stops estrogen production, allowing these patients to take hormone therapies typically reserved for postmenopausal women. Common ovarian suppression medications include goserelin and leuprolide.

How effective is hormone therapy for breast cancer?

According to Dr. Prasad, hormone therapy significantly reduces the risk of recurrence and mortality, with relative risk reductions of up to 65% for breast cancer incidence and 57% for breast cancer death, depending on the specific agent and patient risk profile.

What is the 'best' hormone therapy for breast cancer?

"There is no 'best' option," Dr. Prasad says. "It depends on whether patients are pre- or post- menopausal and their underlying medical issues to determine which of the four therapies is most appropriate."

How is hormone therapy given for breast cancer?

Dr. Prasad says that most hormone therapies are prescribed as pills, except for Faslodex (fulvestrant), which is given as an injection.

How long does hormone therapy treatment usually last?

"Hormone therapy usually lasts at least five years and can extend up to ten years, depending on the patient's and tumor's characteristics," Dr. Prasad explains. "For metastatic breast cancer, the treatment is lifelong."

Can someone skip hormone therapy after lumpectomy?

Dr. Prasad notes that skipping hormone therapy after surgically removing breast cancer depends on the specific characteristics of the cancer. Hormone therapy is not used if the breast cancer is hormone receptor-negative.

Side effects of hormone therapy

Side effects are not universal, according to Dr. Prasad, but the most common include muscle pain (myalgias), decreased bone mineral density and hot flashes. Some patients may also experience sexual dysfunction and weight gain.

What foods should I avoid with hormonal breast cancer?

According to Dr. Prasad, a diet rich in vegetables, fruits, whole grains and fish is recommended. It is best to avoid red and processed meat intake, refined grains and added sugars.

"Evidence suggests that an active lifestyle, healthy diet, limited alcohol intake and achieving and maintaining an ideal body weight (20–25 BMI) may lead to optimal breast cancer outcomes," Dr. Prasad advises.

Does hormone therapy affect the immune system?

"Patients on endocrine therapy are not considered to be immunocompromised like chemotherapy patients," Dr. Prasad says. "Ongoing research is exploring the true effects of these medications on the immune system."

Does hormone therapy for breast cancer cause hair loss?

Aromatase inhibitors, tamoxifen and certain SERMs are most associated with hair thinning, but depending on the individual, they may also cause hair loss. A systematic review found the overall incidence of any level of hair loss in patients receiving endocrine therapies to be 4.4%.