125P Suboptimal ovarian suppression during adjuvant endocrine therapy for premenopausal women with breast cancer: An exploratory analysis of the PREFER and GIM 23 studies

Adjuvant endocrine therapy (ET) with exemestane combined with LHRH analog (LHRHa) is standard of care for premenopausal women with hormone receptor-positive breast cancer. However, LHRHa may not always achieve complete ovarian suppression in these patients. The PREFER-Fertility (NCT02895165) and GIM 23-POSTER (NCT05730647) are prospective, observational studies that enrolled premenopausal women eligible to receive (neo)adjuvant chemotherapy and/or ET. We conducted an exploratory analysis of patients achieving suboptimal suppression of ovarian function enrolled at the coordinating center of both studies, defined as estradiol levels greater than 25.1 ng/L or resumption of menstruation at least 3 months after the start of exemestate plus LHRHa. As of February 2024, a total of 1616 patients were enrolled (766 in the PREFER and 850 in the GIM 23), of whom 528 patients included from the main center. Among them, 26 (4.9%) had a suboptimal ovarian suppression. Median age of these patients was 39 (interquartile range (IQR) 36-46). Median body mass index was 21.8 kg/m2 (84.6% <25). Main histopathological characteristics are summarised in the table. 65.4% of these patients received chemotherapy, mainly anthracycline plus taxane (93.8%), and 3 patients received adjuvant abemaciclib. Median time from last chemotherapy to suboptimal ovarian suppression was 7 months, with 17 patients already on LHRHa during chemotherapy. Monthly leuprorelin was given in 65% of the cases, while the others received monthly triptorelin. Median time to suboptimal ovarian suppression was 7 months (IQR: 5-20). At median follow-up of 5 years (IQR: 2-6), 3 patients had a relapse of disease.Table: 125PCharacteristicsN of patients (%)TNM - StageIA14 (53.9)IB3 (11.5)IIA5 (19.2)IIB2 (7.7)IIIA2 (7.7)Grading11 (3.8)218 (69.3)35 (19.2)NA2 (7.7)HistologyDuctal21 (80.8)Lobular1 (3.8)Other4 (15.4)Ki67<2012 (46.2)≥2014 (53.8)HER2 status012 (46.1)1+5 (19.2)2+2 (7.7)2+ FISH amplified or 3+7 (27) Open table in a new tab In our cohort, almost 5% of premenopausal patients did not achieve ovarian suppression with LHRHa. Oncologists should be aware that serial monitoring of estradiol levels should be performed to address this.