Time to Response: Comparison of Fulvestrant and Oral Endocrine Agents

BackgroundThe different pharmacokinetic profiles of the intramuscularly administered antioestrogen fulvestrant and oral endocrine treatments have led to speculation among some physicians that this could result in a delayed time to response (TTR) with fulvestrant.Patients and MethodsAn analysis of TTR was performed on data from 2 phase III trials comparing fulvestrant and anastrozole as second-line treatments for postmenopausal women with advanced-stage, tamoxifen-resistant breast cancer.ResultsIn a combined analysis of the data from these trials, median TTR was 3.1 months (range, 0.9-33.1 months) for fulvestrant and 3 months (range, 0.7-20.2 months) for anastrozole, although responses were still being noted after 2-3 years of stable disease in some patients. Data were subsequently analyzed from 3 other randomized phase III trials of fulvestrant, anastrozole, and tamoxifen in postmenopausal women. Time to response was also similar between the 3 treatments in these additional analyses.ConclusionTime to response is similar between fulvestrant and oral endocrine treatments, despite pharmacokinetic differences.