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Breast Cancer: Hormone Therapy

By , Caring.com senior editor
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Hormone therapy for breast cancer treatment

One of the most important test results doctors look at when treating a woman with breast cancer is whether her tumor cells contain receptors for the hormones estrogen and progesterone. If present, these hormones can fuel cancer cell growth, and hormone therapy -- which stops them -- can be a very effective weapon in the treatment arsenal.

The presence of receptors

ER positive means tumor cells have receptors for estrogen, and PR-positive means the tumor has progesterone receptors. About 75 percent of breast cancers are estrogen-receptor positive and of those, about 65 percent are also PR-positive. These hormones can fuel rapid cancer cell growth, so the goal is to "turn off" this action by blocking the receptors.

Despite the similar names, hormone therapy is not the same as Hormonal Replacement Therapy, or HRT, which many women take during and after menopause. In fact, HRT isn't considered safe for women with breast cancer.

Which hormone therapy drugs are best?

For years, tamoxifen (brand name Nolvadex, though it's now a generic) was the standard drug of choice for women with hormone-receptor-positive breast cancer. Tamoxifen is a type of drug known as a SERM, which stands for selective estrogen-receptor modulator.

There are newer SERMs being studied and introduced for breast cancer. Raloxifene (brand name Evista) was developed to treat osteoporosis but has been shown to work well for invasive breast cancer. Another SERM, Toremifene (brand name Fareston), is similar to tamoxifen but is rarely used in the U.S., though it's popular in Europe. But tamoxifen is by far the most widely used and prescribed.

New drugs for postmenopausal women

Aromatase inhibitors

Many cancer specialists now believe that a new group of drugs called aromatase inhibitors work better than tamoxifen in postmenopausal women. Several large clinical trial results have been published since 2007 showing that aromatase inhibitors are more effective at preventing recurrence and have fewer side effects.

The reason seems to be that in postmenopausal women, most estrogen is no longer produced by the ovaries but, rather, is converted from another hormone, androgen. Aromatase inhibitors work by preventing the enzyme aromatase from triggering the androgen into estrogen conversion. The names of the drugs are letrozole (brand name Femara), anastrozole (brand name Arimidex), and exemestane (brand name Aromasin).

An even more recent drug

Estrogen-receptor antagonists have recently come into use, and, like SERMs, they block estrogen. However, only one, fulvestrant (brand name Faslodex), has won FDA approval, and it's used solely when other types of hormone therapy have failed.

How hormone therapy is delivered

Tamoxifen, the most common hormone therapy, is taken as a pill every day for five years. This may seem like an eternity, but studies have shown that it can prevent or postpone recurrence if taken over a long period of time. Aromatase inhibitors are usually taken the same way, orally every day for five years.

Are there side effects or risks from hormone therapy?

By blocking or turning off estrogen, hormone therapy causes symptoms similar to menopause, though it doesn't cause actual menopause. These include hot flashes and night sweats, vaginal dryness and itchiness, headache, and fluid retention or weight gain.

Premenopausal women may also develop irregular periods. Tamoxifen causes more of these types of symptoms than do aromatase inhibitors. In addition, tamoxifen has been linked with an increased risk of stroke, blood clots, cataracts, and uterine cancer. Aromatase inhibitors have fewer side effects, but this type of hormone therapy can cause joint pain and decreased bone density.