Concomitant tamoxifen or letrozole for optimal oocyte yield during fertility preservation for breast cancer: the TAmoxifen or Letrozole in Estrogen Sensitive tumors (TALES) randomized clinical trial.

PURPOSE: To determine whether concomitant tamoxifen 20 mg with gonadotropins (tamoxifen-gonadotropin) versus letrozole 5 mg with gonadotropins (letrozole-gonadotropin) affects mature oocyte yield. METHODS: Open-label, single-institution, randomized trial. Inclusion criteria included the following: females, ages 18-44 years old, with new diagnosis of non-metastatic breast cancer, who were undergoing fertility preservation with either oocyte or embryo cryopreservation. Those with estrogen-receptor-positive (ER+) breast cancer were randomized to tamoxifen-gonadotropin or letrozole-gonadotropin. Another group with estrogen-receptor-negative (ER-) breast cancer was recruited, as a prospectively collected comparison arm who took neither letrozole nor tamoxifen (gonadotropin only). The primary outcome was the number of mature oocytes obtained from the cycle. The randomized groups were powered to detect a difference of three or more mature oocytes. RESULTS: Forty-five patients were randomized to tamoxifen-gonadotropin and fifty-one to letrozole-gonadotropin. Thirty-eight patients completed gonadotropin only. Age, antral follicle count, and body mass index were similar between the randomized groups. Our primary outcome of mature oocyte yield was similar between the tamoxifen-gonadotropin and letrozole-gonadotropin groups (12±8.6 vs. 11.6±7.5, p=0.81, 95%CI of difference =-2.9 to 3.7). In a pre-specified secondary comparison, mature oocyte yield was also similar with tamoxifen-gonadotropin or letrozole-gonadotropin versus gonadotropin only (12±8.6 vs. 11.6±7.5 vs. 12.4±7.2). There were no serious adverse events in any of the groups. CONCLUSIONS: Tamoxifen-gonadotropin and letrozole-gonadotropin produced a similar number of mature oocytes. Women who received either tamoxifen-gonadotropin or letrozole-gonadotropin had a similar number of oocytes to the gonadotropin-only group. TRIAL REGISTRATION: NCT03011684 (retrospectively registered 1/5/2017, after 9% enrolled).