Effects of letrozole or tamoxifen coadministered with a standard stimulation protocol on fertility preservation among breast cancer patients

Purpose: To assess the effects of letrozole or tamoxifen coadministration on fertility preservation treatment outcomes. Methods: Retrospective cohort study of 118 breast cancer patients undergoing fertility preservation treatment between 2008 and 2018. Patients who received letrozole (n = 36) or tamoxifen (n = 30) were compared to controls (n = 52) who underwent standard ovarian stimulation protocols. The primary outcome measures included the number of retrieved oocytes, mature oocytes (MII), fertilization, and top-quality embryo rates. The secondary outcome measures included duration of stimulation, gonadotropin dose and peak estradiol level. Results: The number of oocytes retrieved, MII oocytes, fertilization rate, duration of stimulation, or gonadotropin dose were similar in the letrozole and tamoxifen groups, compared to controls. Top-quality embryo rate was lower in the tamoxifen group compared to controls (25% vs 39.4%, respectively, P = 0.034). The abnormal fertilization rate was higher in the letrozole group compared to controls (7.8% vs 3.60%, respectively, P = 0.015). A stepwise logistic regression analysis revealed that letrozole and peak estradiol were significantly associated with abnormal fertilization (OR 11.94; 95% CI 2.35–60.4, P = 0.003 for letrozole and OR 1.075; 95% CI 1.024–1.12, P = 0.004 per 100 unit change in estradiol). Conclusions: There may be a negative effect of letrozole or tamoxifen on fertilization and embryo quality, in fertility preservation cycles. Further studies are needed to confirm these findings.