In a small study, researchers found that giving estradiol, a form of estrogen, to 66 postmenopausal women being treated for advanced-stage, hormone-receptor-positive breast cancers that had stopped responding to aromatase inhibitors (a type of hormonal therapy) was effective on about 30% of the cancers.
This study was a phase II trial, which means the treatment being studied was given to a small number of people to make sure it works and to study its safety. If the results from a phase II trial look promising, researchers will conduct phase III trials, which means the new treatment is given to a larger group of people (more than 1,000) to confirm that it works and to see whether it's more effective than commonly used treatments.
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.
The researchers split the women into two groups:
- 32 women got 30 mg per day of estradiol
- 34 women got 10 mg per day of estradiol
About 30% of the women in each group got benefits from the estradiol (19 women total). But the group that got the higher dose of estradiol had more side effects and the side effects were more severe.
Seven of the cancers that grew during estradiol treatment were treated again with an aromatase inhibitor. Three of the cancers responded to the aromatase inhibitor, even though before the estradiol treatment the cancers had stopped responding to aromatase inhibitors. This suggests that alternating the type of hormonal therapy medicine may cause some hormone-receptor-positive cancers that stop responding to hormonal therapy to start responding again.
Since the benefits were the same with both levels of estradiol, the researchers said the low dose of estradiol makes more sense.
Three kinds of hormonal therapy medicines are used often to treat women diagnosed with hormone-receptor-positive, advanced-stage breast cancer: aromatase inhibitors, Faslodex (chemical name: fulvestrant), and tamoxifen.
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 and tamoxifen work 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 Breastcancer.org Hormonal Therapy section.