Received June 25, 2019
Accepted December 30, 2019

Background: Patients submitted to oncological fertility preservation with letrozole and gonadotropins seems to present a higher rate of immature oocytes and lower fertilization rate in comparison to infertile patients submitted to IVF cycles with gonadotropins. The aim of this study was to evaluate the influence of letrozole on oocyte morphology in breast cancer patients submitted to fertility preservation. Methods: Retrospective analysis performed at a tertiary hospital in Brazil. We evaluated 750 oocytes retrieved from breast cancer patients (n=69) submitted to ovarian stimulation with letrozole and gonadotropins and 699 oocytes from patients without breast cancer (n=92) submitted to ovarian stimulation for in vitro fertilization only with gonadotropins due to male factor infertility. The mature oocytes retrieved were analysed for the presence of refractile bodies, color and regularity of the ooplasm, central granulation degree, cortical granules, zona pellucida staining and regularity, perivitelline space, presence of vacuoles or abnormal smooth-surfaced endoplasmic reticle and oocyte retraction. Results: It was observed a higher incidence of in oocyte dysmorphisms in the letrozole group compared to the control group: increased perivitelline space (p=0.007), irregular zona pellucida (p<0.001), refractile bodies (p<0.001), dark ooplasm (p<0.001), granular ooplasm (p<0.001), irregular ooplasm (p<0.001) and dense central granulation (p<0.001). Conclusion: Coadministration of letrozole was shown to be a risk factor for oocyte dysmorphisms. However, clinical impact of ovarian stimulation protocol with combined use of gonadotropins and letrozole for fertility preservation remains unclear in this setting. These data underline the importance of determining predictive potential of morphological dysmorphisms of human oocytes in IVF outcomes.