Faslodex (chemical name: fulvestrant) is an estrogen receptor downregulator (ERD), a type of hormonal therapy. Faslodex blocks the effect of estrogen on breast tissue by sitting in the estrogen receptor in breast cells.
Right now, Faslodex is approved by the U.S. Food and Drug Administration (FDA) to treat postmenopausal women diagnosed with metastatic, hormone-receptor-positive breast cancer that has stopped responding to other hormonal therapy medicines.
Faslodex is a liquid given as an injection into a muscle.
Arimidex (chemical name: anastrozole) 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.
A study has found that women diagnosed with hormone-receptor-positive, locally advanced or metastatic disease had a lower risk of the cancer growing if they got Faslodex as a first hormonal therapy compared to women who got Arimidex.
The study was presented at the 2016 European Society for Medical Oncology Conference. Read the abstract of “FALCON: A phase III randomized trial of fulvestrant 500 mg vs. anastrozole for hormone receptor-positive advanced breast cancer.”
Locally advanced breast cancer is breast cancer that has spread beyond the breast to nearby tissues, such as the skin or the chest wall. Both locally advanced breast cancer and metastatic breast cancer are considered advanced-stage disease.
Doctors are always trying to figure out which medicines best treat different types of breast cancer. While Faslodex isn’t currently approved to be used as the first medicine to treat advanced-stage, hormone-receptor-positive disease, the researchers thought it might be a good treatment and decided to compare it to the current standard treatment, Arimidex.
In the study, called FALCON, 462 postmenopausal women diagnosed with hormone-receptor-positive, HER2-negative locally advanced or metastatic breast cancer were randomly assigned to one of two medicines as the first hormonal therapy treatment after the advanced-stage disease was diagnosed:
- 230 women got Faslodex
- 232 women got Arimidex
About 87% of the women had metastatic disease.
Of the women who had metastatic disease, just over half in each treatment group had visceral metastases (meaning the cancer had spread to an internal organ, such as the liver or lungs):
- 58.7% of women in the Faslodex treatment group had visceral metastases
- 51.3% of women in the Arimidex treatment group had visceral metastases
The researchers compared progression-free survival between the two treatment groups. Progression-free survival is how long the women lived without the cancer growing.
Progression-free survival was about 3 months longer for women treated with Faslodex compared to women treated with Arimidex:
- Women treated with Faslodex lived for about 16.6 months without the cancer growing.
- Women treated with Arimidex lived for about 13.8 months without the cancer growing.
This difference was statistically significant, which means it was probably because of the difference in treatment and not just due to chance.
The researchers found that women with no visceral metastases got noticeably more benefits from Faslodex than Arimidex. There was little difference in progression-free survival in women who had visceral metastases no matter which treatment they got.
"The phase III FALCON study met its primary endpoint, demonstrating a statistically significant improvement in progression-free survival for [Faslodex] versus [Arimidex]," said Matthew Ellis, M.D., Ph.D., of the Baylor College of Medicine, who presented the study. "The primary analysis was supported by secondary efficacy endpoints. The treatment effects were largely consistent across prespecified patient subgroups, with the largest treatment effect seen in patients without visceral disease."
The results of the FALCON study are very promising and support the results of the earlier FIRST study, which strongly suggested that women diagnosed with hormone-receptor-positive, advanced stage disease had better survival when they got Faslodex as a first hormonal therapy rather than Arimidex.
If you’ve been diagnosed with advanced-stage, hormone-receptor-positive breast cancer, you and your doctor will consider a number of treatment options, including hormonal therapy and chemotherapy. If you haven’t been treated with hormonal therapy for advanced-stage disease yet, you might want to talk to your doctor about this study and whether Faslodex might be a good first treatment choice for you, depending on your unique situation. Together, you and your doctor will decide on a treatment plan that’s best for you.
Editor's note: Since this study was published, the use of Faslodex has been expanded. On Aug. 28, 2017, the U. S. Food and Drug Administration approved a broader use of Faslodex to treat breast cancer. Faslodex can now be used alone as the first treatment for postmenopausal women diagnosed with hormone-receptor-positive, HER2-negative, advanced-stage breast cancer that hasn’t been treated with hormonal therapy.