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Fulvestrant 500 mg shows promise for HR+ breast cancer treatment
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33rd Annual San Antonio Breast Cancer Symposium
SAN ANTONIO — A 500 mg formulation of fulvestrant yielded a 35% shorter time to progression than anastrozole 1 mg in women with hormone-receptor positive breast cancer.
John Robertson, MD, of the University of Nottingham in the UK, noted previous evidence that fulvestrant 250 mg is comparable but not superior to anastrozole as second-line endocrine therapy for advanced HR+ breast cancer in postmenopausal women.
“Other biological and clinical data suggest that fulvestrant 500 mg showed a significant improvement over 250 mg in terms of survival outcomes and time to progression,” he said.
The phase 2, randomized, open-label, multicenter study compared two regimens: intramuscular fulvestrant 500 mg (500 mg on day 0, then 500 mg on days 14 and 28 and every 28 days thereafter) with oral anastrozole (1 mg/day). There were 102 patients in the fulvestrant arm and 103 patients in the anastrozole arm.
“Data from an updated analysis show us that 69% of patients had progressed,” Robertson said. The current analysis was performed when 79.5% of patients had discontinued study treatment.
Median time to progression was 23.4 months for the fulvestrant 500 mg group and 13.1 months in the anastrozole group. The corresponding reduction in risk of progression was 35% (HR=0.66; 95% CI, 0.47-0.92).
“The curves begin to separate at 6 months in terms of resistance and time to progression,” Robertson said.
The median time to treatment failure was 17.6 months in the fulvestrant arm and 12.7 months in the anastrozole arm, representing an HR of 0.73 (95% CI, 0.54-1.00).
The response to subsequent therapy — defined as a complete or partial response — was 23.8% in the fulvestrant group and 21.1% in the anastrozole group.
Fulvestrant 500 mg was well-tolerated and no new safety concerns were documented, according to study results.
“These data provide support that there is a significant time to progression benefit for fulvestrant 500 mg over anastrozole as first-line therapy for HR-positive advanced breast cancer patients,” Robertson said. “The effectiveness may be related to the different mechanism of fulvestrant.”
Primary analysis results indicated that fulvestrant 500 mg was at least as effective as anastrozole in terms of clinical benefit rate and objective response rate. – by Rob Volansky
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