Patients enrolled in this study undergo standard or "random start" ovarian stimulation with Gonadotropins using antagonist protocol before the beginning of chemotherapy. Ovulation is triggered in all patients with a GnRH agonist.
After retrieval, oocytes are denuded and matured oocytes are subjected to fertilization before embryo freezing or direct vitrification.
Primary objective is to evaluate the efficacy of performing a controlled ovarian stimulation with or without letrozole in young women with newly diagnosed breast cancer who are candidates to receive (neo)adjuvant chemotherapy in terms of mature oocytes collected.

