Relative Potencies of Anastrozole and Letrozole to Suppress Estradiol in Breast Cancer Patients Undergoing Ovarian Stimulation before in Vitro Fertilization

Context: Breast cancer patients undergoing controlled ovarian hyperstimulation (COH) for embryo or oocyte cryopreservation should be induced by the method that leads to the least increase in estradiol (E2) levels. Objective: The aim of the study was to determine the potency of anastrozole to suppress serum E2 levels in breast cancer patients undergoing COH. Design and Setting: A prospective sequential cohort study was conducted in an academic center for reproductive medicine between May 2003 and November 2005 for letrozole and between December 2005 and April 2006 for anastrozole. Patients: Breast cancer patients presenting for fertility preservation participated in the study. Intervention: COH using FSH and letrozole (n = 47) or anastrozole (n = 7) was followed by oocyte retrieval and embryo cryopreservation. Main Outcome Measures: Serum E2 levels, area under the curve for E2, and outcomes of COH cycles were measured. Results: There were no significant differences between the two groups regarding length of stimulation, total gonadotropin dose, number of follicles larger than 17 mm, and the lead follicle size on human chorionic gonadotropin (hCG) day and number of embryos cryopreserved. The mean E2 levels on the day of hCG and post-hCG days were higher in the anastrozole group compared to the letrozole group (1325.89 ± 833.17 and 2515.07 ± 1368.52 vs. 427.78 ± 278.24 and 714.38 ± 440.83 pg·d/ml; P ≤ 0.01), respectively, even when anastrozole dose was increased up to 10 mg/d. The mean area under the curve was significantly higher in the anastrozole group compared to the letrozole group (4402.93 ± 1526.7 vs. 1287.48 ± 732.17 pg·d/ml; P <0.004). Conclusions: Breast cancer patients who underwent ovarian stimulation with anastrozole had a significantly higher exposure to E2 than those who were stimulated with letrozole.