Faslodex and Arimidex Better Than Arimidex Alone as First Treatment for Hormone-Receptor-Positive Metastatic Breast Cancer

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Adding Faslodex (chemical name: fulvestrant) to Arimidex (chemical name anastrozole) as the first treatment for metastatic hormone-receptor-positive breast cancer improved overall survival by nearly 8 months compared to Arimidex alone, according to a study.

The research was published in the March 28, 2019, issue of The New England Journal of Medicine. Read the abstract of “Overall Survival with Fulvestrant plus Anastrozole in Metastatic Breast Cancer.”

Study background

Faslodex is an estrogen receptor downregulator, a type of hormonal therapy. Faslodex blocks the effect of estrogen on breast tissue by sitting in the estrogen receptor in breast cells. Faslodex is given as an injection into a muscle.

When this study started in 2004, Faslodex was approved by the U.S. Food and Drug Administration (FDA) to treat postmenopausal women diagnosed with metastatic hormone-receptor-positive breast cancer that had stopped responding to other hormonal therapy medicines. In August 2017, the FDA broadened the approved use of Faslodex so it could be used alone as the first treatment for postmenopausal women diagnosed with hormone-receptor-positive, HER2-negative, advanced-stage breast cancer that hadn’t been treated with hormonal therapy.

Arimidex is an aromatase inhibitor, another type of hormonal therapy. Aromatase inhibitors work by blocking the enzyme aromatase, which turns androgen hormones into small amounts of estrogen in the body. This means that less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells.

Aromatase inhibitors can't stop the ovaries from making estrogen, so aromatase inhibitors only work in postmenopausal women.

Arimidex is approved by the FDA to treat postmenopausal women diagnosed with hormone-receptor-positive breast cancer that is early-stage, advanced-stage, or metastatic.

Arimidex is a pill taken by mouth.

Metastatic breast cancer is breast cancer that has spread to a part of the body away from the breast, such as the bones or liver.

Overall survival is how long the women lived, whether or not the cancer grew.

It’s important to know that since this study started, a new class of targeted therapy medicines, called CDK4/6 inhibitors, has been approved to treat metastatic hormone-receptor-positive, HER2-negative breast cancer. Ibrance (chemical name: palbociclib), Kisqali (chemical name: ribociclib), and Verzenio (chemical name: abemaciclib) are CDK4/6 inhibitors used to treat metastatic breast cancer.

Studies have shown that the CDK4/6 inhibitors in combination with an aromatase inhibitor offer longer progression-free survival for women diagnosed with metastatic hormone-receptor-positive breast cancer compared to hormonal therapy alone. Progression-free survival is how long the women lived before the cancer grew.

Many doctors opt for a combination of a CDK4/6 inhibitor and an aromatase inhibitor as the first treatment for metastatic hormone-receptor-positive disease.

How this study was done

The study, called SWOG S0226, included 694 postmenopausal women diagnosed with metastatic hormone-receptor-positive breast cancer. As a first treatment for metastatic disease, the women were randomly assigned to receive one of two treatments:

  • Faslodex plus Arimidex (349 women)
  • Arimidex alone (345 women)

Half the women were followed for more than 7 years, and half were followed for shorter periods of time. In the Faslodex plus Arimidex group:

  • 29% of the women were still alive
  • half the women lived longer than 49.8 months and half the women lived for shorter periods of time

In the Arimidex alone group:

  • 24% of the women were still alive
  • half the women lived longer than 42 months and half the women lived for shorter periods of time

This 7.8-month difference in overall survival was statistically significant, which means that it was likely due to the difference in treatment and not just because of chance.

The researchers also looked at specific subgroups to see who benefited the most from the Faslodex-Arimidex combination.

Among women who had never been treated with tamoxifen — 60% of the women in the study — overall survival was 52.2 months for women treated with the Faslodex-Arimidex combination compared to 40.3 months for women treated with Arimidex alone.

Among women who were disease-free for at least 10 years from the time of initial diagnosis — 29.8% of women in the study — overall survival was 65.4 months for women treated with the Faslodex-Arimidex combination and 49.7 months for women treated with Arimidex alone.

“Women who received fulvestrant, right up front, lived longer based on this new long-term analysis,” said Rita Mehta, M.D., of the University of California, Irvine, who was the lead author of the study. “This is credible evidence that combination endocrine therapy should be considered an option for first-line treatment of advanced hormone-receptor-positive breast cancer.”

“The combination therapy in this trial provides another option for patients with estrogen-receptor-positive, metastatic breast cancer, and I think also demonstrates that survival is improving for these patients as we gain more options for treatment,” Jennifer Litton, M.D., of the MD Anderson Cancer Center in Houston, who was not involved with the study, said in an interview.

“Clinically, when considering first-line therapy, an endocrine agent plus CDK inhibitor still will likely be the preferred first choice given the very prolonged median [progression-free survival],” she added, but said that the combination of Faslodex and Arimidex does provide an option, especially for people who can’t receive CDK4/6 inhibitors as a first treatment for metastatic disease.

What this means for you

The results of this study support other research, including the FALCON study, suggesting that Faslodex may be a better first treatment option than Arimidex for postmenopausal women diagnosed with metastatic hormone-receptor-positive breast cancer.

If you’re a postmenopausal woman who has been diagnosed with metastatic hormone-receptor-positive breast cancer, you and your doctor will consider a number of treatment options, including hormonal therapy and targeted therapy. If you are deciding on a first treatment for metastatic disease, you may want to talk to your doctor about this study and whether Faslodex is a good choice for you. You also may want to ask whether a CDK4/6 inhibitor in combination with an aromatase inhibitor makes sense for your unique situation. Together, you and your doctor will decide on a treatment plan that’s best for you.

To talk with others who have been diagnosed with metastatic breast cancer, join the Breastcancer.org Discussion Board forum Stage IV/Metastatic Breast Cancer ONLY.

Written by: Jamie DePolo, senior editor

Reviewed by: Brian Wojciechowski, M.D., medical adviser


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