Different dosage forms of gonadotropin-releasing hormone agonist with endocrine therapy in premenopausal hormone receptor-positive breast cancer

Background: Despite the wide use of a 3-month gonadotropin-releasing hormone (GnRH) agonist for ovarian function suppression in premenopausal breast cancer patients, it remains unclear whether it is as effective and safe as a 1-month GnRH agonist regimen when combined with selective estrogen receptor modulators or aromatase inhibitors, especially in younger patients. Methods: This retrospective cohort study included 1109 premenopausal hormone receptor-positive breast cancer patients treated with GnRH agonist plus selective estrogen receptor modulator or aromatase inhibitor. The estradiol (E2) inhibition rate within 1-24 months after treatment with 1-month or 3-month GnRH agonist in cohorts and different subgroups was analyzed. Results: Following 1:1 propensity score matching, 950 patients with a mean age of 39 years and a median follow-up of 46 months were included. Both the 1-month and 3-month groups achieved more than 90% E2 inhibition within 24 months (94.53% vs 92.84%, with a 95% confidence interval for the difference ranging from -4.78% to 1.41%), confirming the noninferiority of 3-month GnRH agonist. Both 1-month and 3-month GnRH agonist rapidly and consistently reduced E2 levels. Of the patients, 60 (6.3%) experienced incomplete ovarian function suppression, with similar rates in the 1-month and 3-month groups (5.5% vs 7.2%). Incomplete ovarian function suppression mainly occurred within the first 12 months, with age younger than 40 years and no prior chemotherapy being the risk factors. Similar disease-free survival and overall survival were found in the 1-month and 3-month groups and in patients with complete and incomplete ovarian function suppression (P > .05). Conclusions: The ovarian function suppression with 3-month GnRH agonist was not inferior to that with 1-month GnRH agonist, regardless of age or combination with a selective estrogen receptor modulator or an aromatase inhibitor.