Time to Response: Comparison of Fulvestrant and Oral Endocrine Agents

Background: The 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 Methods: An 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. Results: In 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. Conclusion: Time to response is similar between fulvestrant and oral endocrine treatments, despite pharmacokinetic differences.