A long-acting, synthetic nonapeptide analog of gonadotropin-releasing hormone (GnRH) with potential anti-tumor activity. Upon administration, histrelin binds to and activates GnRH receptors; prolonged administration results in pituitary GnRH receptor desensitization and inhibition of follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion, leading to a significant decline in testosterone production in males and may inhibit androgen receptor-positive tumor progression; in females, prolonged administration results in decreased estradiol production.