In 2001, Mitwally and Casper introduced letrozole ( a third generation non steroidal aromatase inhibitor licensed for treatment of hormonally-responsive breast cancer after surgery ) as new ovulation induction agent in clomiphene citrate resistant patients with polycystic ovary syndrome (PCOS) . Subsequent studies confirmed the effectiveness of letrozole in induction of ovulation in women with PCOS and in superovulation (either alone or in combination with gonadotropins ) .