Estradiol May Make Breast Cancer Start Responding to Aromatase Inhibitors Again

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Hormonal therapy medicines either block the effect of estrogen on hormone-receptor-positive breast cancer cells or limit the amount of estrogen produced in the body. Over time, some hormone-receptor-positive, advanced-stage breast cancers that responded to hormonal therapy stop responding.

A small study found that giving estradiol, a form of estrogen, to women being treated for advanced-stage, hormone-receptor-positive breast cancers that had stopped responding to hormonal therapy caused about 30% of the cancers to stabilize or start responding to treatment again. In some cases the cancers began to respond to hormonal therapy again. The research was presented at the 2008 San Antonio Breast Cancer Symposium.

Half of the women participating in the study were given a high dose (30 mg.) of estradiol after the breast cancer stopped responding to an aromatase inhibitor, a type of hormonal therapy medicine. The other half of the women were given a low dose (6 mg.) of estradiol. The amount of estradiol a woman received didn't seem to affect the chances of responding to the treatment:

  • 28% of the women who got high-dose estradiol had a response to the treatment
  • 29% of the women who got low-dose estradiol had a response

The researchers aren't sure exactly how estradiol helped some women with advanced-stage breast cancer.

Although most women in this study had no serious side effects from the estradiol, the higher dose was more likely to cause side effects:

  • 34% of the women who took the higher of dose estradiol had serious side effects
  • only 12% of the women who took the lower dose of estradiol had serious side effects

Possible serious side effects of estradiol treatment include:

  • nausea
  • vomiting
  • low blood sodium levels
  • fluid buildup around the lungs

Since the benefits were the same with both levels of estradiol, the researchers said the low dose of estradiol makes more sense.

Two kinds of hormonal therapy medicines are used often to treat women diagnosed with hormone-receptor-positive, advanced-stage breast cancer: aromatase inhibitors and Faslodex (chemical name: fulvestrant).

Aromatase inhibitors work by lowering the amount of estrogen in the body. The aromatase inhibitors are:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

Faslodex works by blocking the effects of estrogen on breast cancer cells.

If you're being treated for hormone-receptor-positive, advanced-stage breast cancer and the cancer has stopped responding to hormonal therapy medicine, consider discussing this study with your doctor. Using estradiol to treat breast cancer isn't routinely done in this situation, and most of the cancers in this study didn't respond to estradiol. Still, as you and your doctor consider your treatment options, the results of this study make it reasonable to consider whether treatment with estradiol might make sense for you.

You can find more information about the different types of hormonal therapy, and how and when they're used to treat both early- and advanced-stage breast cancer in the Hormonal Therapy section.

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