Gonadotropin-releasing hormone (GnRH) agonists

Gonadotropin-releasing hormone (GnRH) agonists, also known as luteinizing hormone-releasing hormone (LHRH) analogs, are part of a class of injectable medicines offered to pre- and perimenopausal women with breast cancer in order to temporarily suppress, or slow, ovarian function. For some women, GnRH agonists are a part of long-term hormonal therapy for breast cancer. When given during chemotherapy these medicines also may protect future fertility.

Ask your doctors to be specific about what kind of ovarian suppression they recommend. Ovarian suppression can involve GnRH agonist medicines or oophorectomy, surgery that permanently removes your ovaries.

Common GnRH agonists are:

• Goserelin (Zoladex)
• Leuprolide (Lupron)
• Triptorelin (Trelstar)

How GnRH agonists work

In premenopausal women, the brain tells the ovaries to develop an egg, called an oocyte, to be released every month. We call the release of the egg ovulation.

Before ovulation, the cells around the developing egg make estrogen. After ovulation, these cells make both estrogen and progesterone.

GnRH agonists tell the brain not to signal the ovaries to develop an egg. Stopping the brain’s signal means that the ovaries do not develop an egg, ovulation does not occur, and estrogen and progesterone are not made.

When the ovaries stop making as much estrogen, breast cancer cells that are estrogen receptor-positive can’t continue to grow.

Who gets GnRH agonists

GnRH agonists are used in two ways:

• As part of treatment for estrogen receptor-positive breast cancer
• To protect future fertility in women getting chemotherapy for breast cancer

Women with estrogen receptor-positive breast cancer who are pre- or perimenopausal may be given GnRH agonists along with tamoxifen or another hormonal therapy to treat breast cancer, depending on the stage of the cancer. Once your ovaries are fully suppressed, your doctor might switch you from tamoxifen to an aromatase inhibitor.

Women getting chemotherapy treatment may also be given GnRH agonists in order to protect future fertility.

How GnRH agonists are given

• Goserelin is given by injection once a month or once every 3 months
• Leuprolide is given by injection once a month or once every 3 months
• Triptorelin is given by injection once a month

Side effects and things to remember

The GnRH agonists may cause a variety of side effects related to low estrogen levels. Remember to talk to your healthcare team about any side effects you may experience, including:

• hot flashes
• night sweats
• insomnia and fatigue
• mood changes
• loss of sexual interest
• bone thinning
• vaginal dryness
• bone pain

After you finish taking a GnRH agonist, your brain will return to signaling your ovaries to start working again, but it may take some time.

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on Side Effects for more information.