Higher Faslodex Dose More Effective Against Metastatic Breast Cancer

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Faslodex (chemical name: fulvestrant) is a type of hormonal therapy medicine used to treat postmenopausal women diagnosed with advanced-stage hormone-receptor-positive breast cancer in two situations:

  • if the cancer failed to respond or stopped responding to another hormonal therapy (tamoxifen, for example)
  • if the cancer is a recurrence of early-stage breast cancer that developed while a woman is taking hormonal therapy

Hormonal therapy medicines working by blocking the effects of estrogen on breast cancer cells or by lowering the amount of estrogen the body produces.

Two studies on Faslodex were presented at the 2009 San Antonio Breast Cancer Symposium. One study found that advanced-stage, hormone-receptor-positive breast cancers treated with 500 mg of Faslodex (double the usual dose) had a slightly better response than cancers treated with 250 mg of Faslodex (the usual dose). The other study found that using Faslodex and Arimidex (chemical name: anastrozole) together was no better than Arimidex alone for treating advanced-stage breast cancer.

Faslodex is an estrogen receptor downregulator (ERD). Like tamoxifen, Faslodex works by blocking estrogen receptors. Faslodex sits in the estrogen receptors in breast cells. If Faslodex is in the estrogen receptor, there is no room for estrogen and it can't attach to the cell. If estrogen isn't attached to a breast cell, the cell doesn't receive estrogen's signals to grow and multiply. Faslodex also:

  • reduces the number of estrogen receptors
  • changes the shape of breast cell estrogen receptors so they don't work as well

In the study that compared the usual dose of Faslodex with double the usual dose, 736 women diagnosed with advanced-stage, hormone-receptor-positive breast cancer had previously been treated with either tamoxifen (called an antiestrogen in the study) or an aromatase inhibitor. Still, the breast cancer came back (recurred) or grew.

Half the women got 250 mg of Faslodex (the standard dose) and the other half got 500 mg of Faslodex. Faslodex is injected into a muscle once a month.

Doctors checked the cancers every 12 weeks to see if the Faslodex was having any effect. The likelihood of the cancer responding to Faslodex was the same for both doses. Still, there were differences in the way the cancers responded to the different doses. Among women who got 500 mg of Faslodex:

  • The cancer didn't grow for about 6.5 months compared to 5.5 months for women who got 250 mg of Faslodex. While small, the difference is statistically significant, which means that it was likely due to the higher dose of Faslodex instead of chance.
  • Overall survival was 16% higher compared to women who got 250 mg of Faslodex. But this difference wasn't statistically significant, which means it could have been due to chance and not because of the different dose of Faslodex.

Side effects and overall quality of life were the same for both groups of women.

These results suggest that Faslodex can be a good hormonal therapy option to treat breast cancer that comes back as advanced-stage disease or advanced-stage breast cancer that progresses after being treated with either tamoxifen or an aromatase inhibitor. The researchers said 500 mg now should be the standard dose.

In the study that compared Faslodex and Arimidex to Arimidex alone, 514 women diagnosed with advanced-stage, hormone-receptor-positive breast cancer had been treated with chemotherapy, hormonal therapy, or both before the cancer grew. Half the women got the aromatase inhibitor Arimidex and the standard dose of Faslodex. The other half got only Arimidex.

Aromatase inhibitors work by reducing the amount of estrogen produced in the body. The aromatase inhibitors are: Arimidex (chemical name: anastrozole), Aromasin (chemical name: exemestane), and Femara (chemical name: letrozole).

There was no difference in response to the two treatments. This suggests that Faslodex is best used by itself after another hormonal therapy medicine doesn't work or stops working.

If you've been diagnosed with advanced-stage, hormone-receptor-positive breast cancer, either as a recurrence or as the initial diagnosis, you and your doctor will consider a number of treatment options, including hormonal therapy and chemotherapy. Because the breast cancer is hormone-receptor-positive, hormonal therapy medicines are still good treatment options even if you've been treated with hormonal therapy in the past. Faslodex, which works differently than tamoxifen and the aromatase inhibitors, might be a good choice, depending on your unique situation. If your doctor does recommend Faslodex, you might want to ask how much you'll receive. If the standard dose (250 mg) is recommended, consider asking your doctor about the first study reviewed here and whether the higher dose (500 mg) makes sense for you. Together, you and your doctor will decide on a treatment plan that is best for you.

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