FDA Approves New Treatment for Tamoxifen-Resistant Breast Cancer

The US Food and Drug Administration (FDA) has granted approval to AstraZeneca’s new breast cancer drug fulvestrant (Faslodex) for treatment of hormone-receptor-positive metastatic breast cancer in postmenopausal women with disease progression following antiestrogen therapy, with, for example, tamoxifen(Drug information on tamoxifen). Fulvestrant is an estrogen-receptor antagonist without known agonist effects. It is the only estrogen-receptor antagonist to be proven effective after tamoxifen failure.

Distinct Hormonal Therapy

Currently, advanced breast cancer patients whose tumors have been shown to depend on hormones to grow may be given drugs such as tamoxifen that act by blocking the estrogen receptor, or aromatase inhibitors that decrease the amount of estrogen in a woman’s body. Fulvestrant is a hormonal therapy that works by binding, blocking, and degrading the estrogen receptor, and does not cause the type of side effects commonly associated with cytotoxic chemotherapy. It is administered as a once-monthly intramuscular injection, which may assist health-care professionals in monitoring compliance, and may also make treatment more convenient for some patients.

"Faslodex provides an effective, new treatment option for women with advanced breast cancer whose tumors have become resistant to tamoxifen," said lead fulvestrant trial investigator C. Kent Osborne, MD, Baylor College of Medicine, Houston. "When you have a new drug like Faslodex that we can now add to that sequence of drugs, we may be able to control the breast cancer for a longer period of time."

Gerard T. Kennealey, MD, vice president of clinical research, oncology, for AstraZeneca, noted, "The management of advanced breast cancer has significantly improved through sequential treatment with different hormonal therapies. The introduction of Faslodex expands the number of options available for sequential treatment and provides women with a new drug that works in a different way."

Phase III Trials Confirm Activity

The FDA approval was based on data from two phase III, randomized, multicenter studies (one in North America and one predominantly in Europe) comparing fulvestrant, 250 mg once monthly injection, to daily 1-mg oral anastrozole(Drug information on anastrozole) (Arimidex) tablets. The total of 851 women enrolled in both trials were postmenopausal with a variety of involved sites (including liver and lung) and had been treated with one prior hormonal therapy—in almost all cases, tamoxifen.