Treatment that influences the level of estrogen in your body can be called either hormone therapy, antihormonal therapy or endocrine therapy. Hormone therapies are ONLY used to treat hormone receptor-positive breast cancers. All healthy breast cells have hormone receptors; but when cancer cells have hormone receptors, a tumor can grow significantly in the presence of certain hormones.

Hormone therapy for breast cancer treatment is different from menopausal hormone replacement therapy (MHT/HRT) used to reduce symptoms of menopause. MHT/HRT is meant to increase hormone levels in the body and can increase the risk of breast cancer if used for more than 5 years. MHT/HRT is only recommended for short-term use to ease menopausal symptoms in women who have not experienced breast cancer.

All tumors are checked for hormone receptors by a pathologist who determines the receptor status of a tumor by testing the tumor tissue removed during biopsy or surgery. Breast cancers with a significant amount of cells that have hormone receptors are called hormone receptor-positive, either estrogen receptor-positive (ER+) and/or progesterone receptor-positive (PR+). Breast cancers that have few or no cells with hormone receptors are hormone receptor-negative (ER- and/or PR-).

Hormone receptive breast cancer is the most common type. An ER+/PR+ tumor is considered less aggressive than a breast cancer that does not express these receptors, because a cancer with hormone receptors may respond better to treatment.

Hormone therapy for breast cancer can be neoadjuvant, to shrink a tumor before an operation making a non-operable cancer operable. More often, hormone therapy is offered after completion of other treatments such as chemotherapy in order to minimize toxicity. Hormone therapy following surgery, radiation or chemotherapy has been shown to reduce the risk of breast cancer recurrence and improve overall survival in people with hormone-sensitive breast cancers. It can also effectively reduce the risk of metastatic breast cancer growth and disease progression in people with hormone-sensitive tumors.

The most common forms of hormone therapy for breast cancer work by either blocking hormones from attaching to cancer cells or by decreasing your body’s production of hormones so the cancer cannot use the body’s own hormones to grow. Options for hormonal therapy differ slightly depending on whether a woman has been through menopause.

Medications that block hormones from attaching to cancer cells and stimulating growth

One type of hormone therapy tries to block hormones from attaching to cancer cells. When hormones cannot attach to cancer cells, a tumor no longer receives a stimulus to grow. That may slow tumor growth and the cancer cells may die. The following drugs have this type of activity:

• Tamoxifen: Usually taken in pill form every day. Used to reduce the risk of cancer recurrence in women who have been treated for early-stage breast cancer. Usually taken for 5 to 10 years. May also be used to treat advanced cancer. Appropriate for both premenopausal women and postmenopausal women.

Medications that stop the other glands in the body from making any estrogen after menopause

Another type of hormone therapy is called aromatase inhibitors (AI). These substances can reduce the amount of estrogen your body makes. Used in women who have undergone menopause — either naturally or as a result of cancer treatment. They include:

• Anastrozole (Arimidex): Taken in pill form every day to reduce the risk of cancer recurrence in womem who have been treated for early-stage breast cancer. It can also treat advanced breast cancer.
• Exemestane (Aromasin): Taken in pill form by women every day to reduce the risk of recurrence after treatment for early-stage breast cancer. Sometimes used after taking tamoxifen for two or three years. Can also treat advanced breast cancer when tamoxifen is no longer working.
• Letrozole (Femara): Taken in pill form every day to reduce the risk of recurrence after treatment for early-stage breast cancer. Can be used alone or given after completing tamoxifen treatment. Also used to treat advanced breast cancer.

Treatments to stop ovarian function in premenopausal women

Women who haven’t undergone menopause may opt for treatment to stop their ovaries from producing hormones. These strategies are generally used with young women with the BRCA mutation or those with aggressive breast cancer. Treatments to stop ovarian function may allow premenopausal women to take medications only available to postmenopausal women.  Options may include:

• Surgery to remove the ovaries (oophorectomy) may offer some women additional protection against recurrence and secondary cancers such as ovarian cancer.
• Treatment with Goserelin (Zoladex) and Lupron: These are Luteinising Hormone Releasing Hormone (LHRH) agonists that stop the ovaries from producing estrogen. They can be used to suppress the ovaries long term.
• Radiation therapy aimed at the ovaries.

Side effects of hormone therapy for breast cancer include: Hot flashes, vaginal discharge, vaginal dryness or irritation, fatigue, nausea, joint and muscle pain, menopause, impotence in men with breast cancer. Less common, more-serious side effects of hormone therapy may include: Blood clots in veins, endometrial cancer or uterine cancer, cataracts, stroke, osteoporosis, and heart disease.

Hormone therapy with tamoxifen and/or aromatase inhibitors is typically prescribed for at least 5 years and up to 10 years. Side effects can sometimes make it difficult to complete hormone therapy. Women who complete the full course have higher rates of survival. Treatment with hormone therapies tamoxifen and/or aromatase inhibitors lowers the risk of breast cancer recurrence by 50%, and decreases new breast cancer in the opposite breast.

Your oncologist will discuss the most appropriate hormonal therapy regimen based on your breast cancer pathology and age. It is very important to take these pills every day adhering to the daily schedule and dosage as planned, otherwise you may reduce the benefit of these drugs.