SAT-141 Timing of Gonadotropin Releasing Hormone Agonist Administration in Premenopausal Women with Breast Cancer

Abstract Disclosure: A. Oostens: None. J. Jansen: None. S. Lie Fong: None. Background: Administration of gonadotropin-releasing hormone agonists (GnRH-a) prior to start of chemotherapy for young women with breast cancer is recommended to prevent premature ovarian insufficiency after treatment. The protective mechanism of GnRH-a is not fully understood. GnRH-a cause a temporary increase of gonadotropins, the "flare-up” effect, which boosts ovarian follicle recruitment and generally lasts several days. Thereafter, GnRH receptors become desensitized leading to suppression of gonadotropin secretion, the so-called downregulation. It remains unclear whether initiation of chemotherapy during the “flare-up” phase may exert a different effect on the ovarian reserve as compared to when chemotherapy is started after down-regulation of gonadotropins.Objective: To review literature on the influence of timing of GnRH-a administration prior to chemotherapy on ovarian reserve, assessed by the most accurate marker serum anti-Müllerian hormone (AMH) levels, in premenopausal patients with breast cancer.Methods: The following keywords: “Breast Cancer” AND “Gonadotropin Releasing Hormone Agonist” AND “Anti-Müllerian Hormone” were used. Literature search was performed in October 2024. Results: Eventually, 8 studies were eligible after screening by two independent reviewers. Two randomized controlled trials and 6 prospective observational studies published between 2017 and 2023 were included. Participants were 1.280 premenopausal women treated for breast cancer stage I-III, aged between 18 and 49 years. In one study, the objective was to measure serum AMH levels with regard to timing of GnRH-a administration on 1-6, 7-13 or at least 14 days prior to the start of chemotherapy. The other 6 studies compared AMH levels after chemotherapy with or without GnRH-a and described the timing of GnRH-a administration as ‘at least 1 week before chemotherapy initiation’ (3 studies), by a mean interval between GnRH-a administration and first dose of chemotherapy of (7.9 +/- 8.3 days and 7.4 +/- 7.2 days in 2 studies) or as ‘GnRH-a was administered within the first week of chemotherapy’. Conclusion: If chemotherapy is started during the expected flare-up phase of GnRH-a for ovarian suppression, current data are insufficient to accurately counsel patients on the possible effect on ovarian reserve. Presentation: Saturday, July 12, 2025