NEW YORK (Reuters Health) – Doubling the standard dose of fluvestrant improves the efficacy of the drug against breast cancer without affecting tolerability, new research suggests. Moroever, at the increased dose, fluvestrant is at least as effective as anastrozole as first-line endocrine therapy for advanced hormone receptor–positive breast cancer in postmenopausal women, according to the report in the Journal of Clinical Oncology for August 24.
The results, lead investigator Dr. John F. R. Robertson told Reuters Health, “suggest that a higher dose of fulvestrant — 500 mg — is more effective than a third generation aromatase inhibitor, although I think the data are not yet sufficient to change clinical practice.”
Dr. Robertson of the University of Nottingham, UK, and colleagues came to this conclusion after an open-label study of 205 patients who were randomized to treatment with the pure antiestrogen fulvestrant or anastrozole. Fulvestrant was given at a dose of 500 mg/month plus 500 mg on day 14 of the first month. Anastrozole was given at 1 mg/day.
The proportion of patients experiencing an objective response or stable disease for at least 24 weeks was 72.5% in the fulvestrant group and 67.0% in the anastrozole group. The corresponding objective response rates were 36.0% and 35.5%. The duration of these responses also favored fulvestrant.
The time to progression was significantly greater for fulvestrant than anastrozole. In fact, the median time to progression was not reached for fulvestrant but was 12.5 months for anastrozole. Both treatments were well tolerated.
“Combined with other data,” concluded Dr. Robertson, “it now appears that fulvestrant 500 mg is more effective than the current 250 mg dose, with no apparent difference in tolerability. Other studies to be reported later this year should provide a definitive answer on the clinical value of fulvestrant 500 mg.”
J Clin Oncol 2009;27.