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BACKGROUND: In this secondary analysis of the TAmoxifen or Letrozole in Estrogen Sensitive tumors (TALES) trial, we aimed to investigate if concurrent administration of letrozole vs. tamoxifen vs. no added treatment affects hormonal composition and size of stimulated ovarian follicles. METHODS: TALES is a randomized controlled trial of IVF stimulation for estrogen receptor (ER)-positive breast cancer patients stimulated with gonadotropins and administered concurrent tamoxifen 20 mg or letrozole 5 mg. We analyzed estradiol (E2), testosterone (T), progesterone (P4), follicle stimulating hormone (FSH), luteinizing hormone (LH), and anti-Mullerian hormone (AMH). We used ANOVA/Kruskal-Wallis, logistic, and linear regression models to examine differences in follicular hormone levels, size, and mature oocyte yield between trial arm. RESULTS: We included data from total 246 follicles (94 letrozole, 82 tamoxifen, and 70 control) from 123 unique participants. E2 was lower (letrozole 187.4, tamoxifen 1026.0, control 821.5 ng/mL, p

PurposeTo determine whether concomitant tamoxifen 20 mg with gonadotropins (tamoxifen-gonadotropin) versus letrozole 5 mg with gonadotropins (letrozole-gonadotropin) affects mature oocyte yield.MethodsOpen-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.ResultsForty-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.ConclusionsTamoxifen-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 registrationNCT03011684 (retrospectively registered 1/5/2017, after 9% enrolled).