A retrospective analysis of the proportion of patients responding for > 1 year in two phase III studies of fulvestrant vs. anastrozole

737 Background: Fulvestrant (Faslodex) is an estrogen receptor antagonist with no agonist effects. Two phase III trials have compared the efficacy of fulvestrant 250 mg (once-monthly, intramuscular injection) and anastrozole (1 mg/daily, p.o.) in patients with advanced breast cancer progressing on prior endocrine therapy. Fulvestrant was at least as effective as anastrozole for the primary endpoint of time to progression and the secondary endpoint of objective response (OR). Here, we report a retrospective analysis of duration of response (DOR) by categorical time period (≥1 year) in patients experiencing an OR (complete [CR] or partial response [PR]) or clinical benefit (CB; CR + PR + stable disease [SD] ≥24 weeks) in these two trials. Methods: Duration of OR and CB was calculated from randomization until disease progression and percentages were calculated using the total number of patients per treatment group as the denominator (fulvestrant n=428; anastrozole n=423). Results: Median follow-up was 22.1 m...