Hormone Therapy

Hormone therapy works by blocking estrogen that causes cell proliferation. It is used only for patients with hormone receptor-positive tumors. Different types of hormone therapy work in different ways by:

• Blocking estrogen receptors in cancer cells (Tamoxifen)
• Suppressing estrogen production in the body (Aromatase inhibitors)
• Destroying ovaries, which produce estrogen (Ovarian ablation)

Tamoxifen was the first widely used hormonal therapy drug, but it has been replaced by aromatase inhibitors for some women. Aromatase inhibitors are used only to treat postmenopausal women. Tamoxifen is mainly used as adjuvant therapy for premenopausal women with hormone-sensitive breast cancer.

Tamoxifen and Selective Estrogen Receptor Modulators (SERMs)

Tamoxifen (Nolvadex) has been the standard hormonal drug used for breast cancer. It belongs to a class of compounds called selective estrogen receptor modulators (SERMs). SERMs chemically resemble estrogen and trick the breast cancer cells into accepting it in place of estrogen. Unlike estrogen, however, they do not stimulate breast cancer cell growth. Because SERMs block estrogen’s effects on cancer cells, they are sometimes referred to as "anti-estrogen" drugs.

Tamoxifen is used for all cancer stages in women of all ages with hormone receptor-positive cancers. In addition, it is used to prevent breast cancer in high-risk women. Another SERM drug, toremifene (Fareston), is an option for women with advanced cancer, but this drug is rarely used in the United States. A third drug, fulvestrant (Faslodex), works in a similar anti-estrogen way to tamoxifen but belongs to a different drug class. Fulvestrant is approved only for postmenopausal women with hormone-sensitive advanced breast cancer in which tamoxifen or aromatase inhibitors no longer work.

To prevent cancer recurrence, women should take tamoxifen for 5 years following surgery and radiation. Tamoxifen is an effective cancer treatment, but it can cause unpleasant side effects and has small (less than 1%) but serious risks for blood clots and uterine (endometrial) cancer. Any signs of vaginal bleeding should be immediately reported to the doctor, as this may be a symptom of uterine cancer.

Less serious, but discomforting, side effects include hot flashes and mood swings. According to a 2007 study, nearly 25% of women stop taking tamoxifen within 1 year because of these symptoms. By 3.5 years, over 33% stop treatment. Taking tamoxifen for fewer than 5 years, however, increases the risk for cancer recurrence and death. Talk with your doctor about antidepressants or other therapies that may help you cope with tamoxifen’s side effects.

Many doctors now recommend that postmenopausal women switch to an aromatase inhibitor after 2 - 3 years of tamoxifen therapy. Several 2007 studies indicated that switching from tamoxifen to an aromatase inhibitor significantly improves survival rates and reduces the risk of death from breast cancer as well as other causes.

Aromatase Inhibitors

Aromatase inhibitors block aromatase, an enzyme that is a major source of estrogen in many major body tissues, including the breast, muscle, liver, and fat. Aromatase inhibitors work in a different way than tamoxifen. Tamoxifen interferes with tumors’ ability to use estrogen by blocking their estrogen receptors. Aromatase inhibitors reduce the overall amount of estrogen in the body.

Because these drugs cannot stop the ovaries of premenopausal women from producing estrogen, they are only recommended for postmenopausal women.

There are currently three aromatase inhibitors approved for treating early-stage, hormone receptor-positive breast cancer in postmenopausal women:

• Anastrazole (Armidex) for treatment after surgery
• Exemestane (Aromasin) for women who have taken tamoxifen for 2 - 3 years
• Letrozole (Femara) for treatment after surgery or for women who have completed 5 years of tamoxifen therapy

All of these drugs are also approved for women with advanced (metastatic) hormone-sensitive breast cancer. Studies indicate that the introduction of aromatase inhibitors has helped greatly in prolonging survival for women with advanced cancer.

Compared to tamoxifen, aromatase inhibitors are less likely to cause blood clots and uterine cancer. However, these drugs are more likely to cause osteoporosis, which can lead to bone loss and fractures. In general, recent studies indicate that aromatase inhibitors are better than tamoxifen in improving survival and reducing the risk of cancer recurrence. Unfortunately, like tamoxifen, they can cause hot flashes, as well as joint pain.

Selective Estrogen Receptor Downregulators (SERDs)

Selective estrogen receptor downregulators (SERDs) block estrogen in all tissues in the body. Fulvestrant (Faslodex) is one such drug, which is proving to be at least as effective as anastrozole in delaying time to disease progression in women with advanced breast cancer. Side effects generally include gastrointestinal problems and hot flashes.

Progestins

Progestins, particularly megestrol (Megace), have been used as second- or third-line treatment of advanced breast cancer when tamoxifen fails. Some of the aromatase inhibitors, however, are proving to be more effective, and some have fewer side effects, such as weight gain.

Ovarian Ablation

Ovarian ablation literally shuts down estrogen production from the ovaries. Medications can accomplish ovarian ablation. Destroying the ovaries with surgery or radiation can also shut down estorgen production. (Osteoporosis is one serious side effect of this approach, but several therapies are available to help prevent bone loss.)

Chemical Ovarian Ablation. Drug treatment (non-chemotherapy drugs) to block ovarian production of estrogen is called chemical ovarian ablation. It is often reversible. The primary drugs used are luteinizing hormone-releasing hormone (LHRH) agonists, such as goserelin (Zoladex). (They are also sometimes called GnRH agonists). These drugs block the release of the reproductive hormones LH-RH, therefore stopping ovulation and estrogen production.

Studies suggest that women with estrogen-positive early stage cancer who take goserelin have similar survival rates to those who take standard chemotherapy. They also experience fewer serious side effects. A major analysis of four trials using LHRH agonists plus tamoxifen suggested that this combination should be the standard for patients with advanced breast cancers that are hormone-receptor positive, although this is an area of controversy. (Chemotherapy is still more effective in women with estrogen-negative tumors.)

Ovariectomy. Ovariectomy, the removal of the ovaries, has modestly improved breast cancer survival rates in some premenopausal women whose tumors are hormone receptor-positive. In these women, combining this procedure with tamoxifen may improve results beyond those of standard chemotherapies. Ovariectomy does not benefit women after menopause, and its advantages can be blunted in women who have received adjuvant chemotherapy. The procedure causes sterility and can have a major negative emotional impact on younger patients.