The U.S. Food and Drug Administration (FDA) has approved the 500mg dose of fulvestrant (Faslodex?, Astra Zeneca) injection, replacing the previously approved monthly dose of 250mg, for the treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following antiestrogen therapy.[1]

Fulvestrant is an oestrogen receptor antagonist, indicated for the treatment of postmenopausal women with oestrogen receptor-positive, locally advanced or metastatic breast cancer for disease relapse on or after adjuvant anti-oestrogen therapy or disease progression on therapy with an anti-oestrogen.

The FDA approval of fulvestrant, 500mg was based on results from CONFIRM (COmparisoN of Faslodex In Recurrent or Metastatic breast cancer), a Phase III study which demonstrated that fulvestrant 500mg significantly reduced the risk of disease progression in patients with metastatic breast cancer, when compared with the 250mg dose. Safety and tolerability profiles of both doses were comparable.[2]

“This approval is an important advancement for women with metastatic breast cancer, where the treatment approach is centered on delaying disease progression,” said Gershon Locker, M.D., Medical Director for AstraZeneca. “Faslodex at 250mg has been an important treatment option for many women, and we now have data to show that the new 500mg dosing regimen can improve progression free survival compared with the 250mg dose.”

The recommended dose of fulvestrant 500mg should be administered intramuscularly into the buttocks as two 250mg injections, one in each buttock, on days 1, 15, 29 and once monthly thereafter. A dose of 250mg is recommended in patients with moderate hepatic impairment.[1]

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According to data from the U.S. National Cancer Institute, more than 207,000 American women will be diagnosed with breast cancer in 2010.[3] Approximately 155,000 women in the United States are currently living with metastatic breast cancer, and this number is projected to increase to nearly 162,000 by the year 2011.

The CONFIRM study, presented for the first time at the annual San Antonio Breast Cancer Symposium (SABCS) in December 2009, showed fulvestrant 500mg reduced the risk of disease progression (assessed as progression free survival) by 20 percent (HR 0.80; 95% CI 0.68-0.94, p=0.006) when compared with fulvestrant 250mg. Fulvestrant 500mg significantly increased median progression free survival to 6.5 months vs. 5.4 months with 250mg (p=0.006).

Objective Response Rates calculated in patients with measurable disease was not significantly different between fulvestrant 500mg (13.8%) and 250mg (14.6%) (HR=0.94; 95% CI: 0.57-1.55) (p=0.795). Median overall survival was 25.1 months with fulvestrant 500mg and 22.8 months with 250mg (HR=0.84; 95% CI: 0.69-1.03) (p=0.091). At the time of analysis, overall survival was not statistically significant. A pre-planned second survival analysis will occur as data mature when approximately 75% of patients have had an event.

The CONFIRM study (COmparisoN of Faslodex In Recurrent or Metastatic breast cancer) was a Phase III, randomized, double-blind, parallel-group, multi-center trial comparing fulvestrant 500 mg (n=362) and 250 mg (n=374) in postmenopausal women with estrogen receptor-positive advanced breast cancer, who progressed or recurred following one prior endocrine therapy (antiestrogen or aromatase inhibitor). Eligible patients were randomized 1:1 to fulvestrant 500mg or 250mg, and assessed for tumor progression every 12 weeks. The primary objective was to compare the efficacy of both treatment groups in terms of progression free survival. Secondary objectives included: objective response rate (ORR), clinical benefit rate (CBR), duration of clinical benefit (DoCB), overall survival and quality of life (QoL). Safety and tolerability were also assessed.

[1] FASLODEX Prescribing Information.
[2] Di Leo A, Jerusalem G, Petruzelka L et al. CONFIRM: Phase III, randomized, parallel-group trial comparing fulvestrant 250 mg vs fulvestrant 500 mg in postmenopausal women with oestrogen receptor-positive advanced breast cancer. San Antonio Breast Cancer Symposium 2009. Abstract 25.
[3] National Cancer Institute. Surveillance Epidemiology and End Results cancer statistics. Web site Accessed August 10, 2010

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