GNRH1 and cancer: Another effect of COS is the prevention of luteinizing hormone (LH) peak, avoiding premature ovulation, which is one of the major causes of cycle cancellations.( 12 - 15 )Traditionally, both gonadotropin-releasing hormone agonist (ag-GnRH) and gonadotrophin-releasing hormone antagonist (ant-GnRH) have been used as injectable medications.( 13 ) In cases of preservation of fertility, especially in cancer patients, the ant-GnRH protocol is generally used.