General Information

Faslodex (fulvestrant) is an estrogen receptor antagonist.

Faslodex is specifically indicated for the treatment of:

• Hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer in postmenopausal women not previously treated with endocrine therapy.
• HR-positive advanced breast cancer in postmenopausal women with disease progression following endocrine therapy.
• HR-positive, HER2-negative advanced or metastatic breast cancer in postmenopausal women in combination with ribociclib, as initial endocrine based therapy or following disease progression on endocrine therapy.
• HR-positive, HER2-negative advanced or metastatic breast cancer in combination with palbociclib or abemaciclib in women with disease progression after endocrine therapy

Faslodex is supplied as an injection for intramuscular injection. Faslodex 500 mg should be administered intramuscularly into the buttocks (gluteal area) slowly (1 - 2 minutes per injection) as two 5 mL injections, one in each buttock, on Days 1, 15, 29, and once monthly thereafter. A dose of 250 mg is recommended in patients with moderate hepatic impairment to be administered intramuscularly into the buttock (gluteal area) slowly (1 - 2 minutes) as one 5 mL injection on Days 1, 15, 29, and once monthly thereafter.

Mechanism of Action

Faslodex (fulvestrant) is an estrogen receptor antagonist. Many breast cancers have estrogen receptors (ER) and the growth of these tumors can be stimulated by estrogen. Fulvestrant is an estrogen receptor antagonist that binds to the estrogen receptor in a competitive manner with affinity comparable to that of estradiol and downregulates the ER protein in human breast cancer cells.

Side Effects

Adverse events reported in clinical testing of Faslodex include (but are not limited to) the following:

• Vomiting
• Nausea
• Constipation
• Pain
• Headache
• Diarrhea
• Hot flushes
• Pharyngitis (throat inflammation)

Clinical Trial Results

The effectiveness of Faslodex was demonstrated in clinical trials comparing the drug to the aromatase inhibitor Arimidex (anastrozole), which works by reducing the amount of estrogen in the body. Two randomized trials in North America and Europe were conducted in postmenopausal women with locally advanced or metastatic breast cancer. The double-blind North American trial included 400 women, while the open, randomized European trial included 451 women. All subjects had progressed after previous therapy with an anti-estrogen or progestin.

Subjects were randomized to receive either Faslodex 250 mg intramuscularly once a month or Arimidex 1 mg orally once a day. All subjects were assessed monthly for the first three months and then every three months thereafter. Results showed that Faslodex was at least as effective as Arimidex. In the North American trial, objective tumor response rates were 17.0% for both the Faslodex- and Arimidex-treated groups. In the European trial, Faslodex produced a 20.3% objective tumor response rate, compared to 14.9% for the Arimidex group. Time to progression for Faslodex versus Arimidex was 5.5 months versus 3.5 months in the North American trial and 5.5 months versus 5.2 months in the European trial.