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Abstract Ovarian function suppression (OFS) benefits young women with hormone receptor (HR)-positive breast cancer but they are at risk for ovarian function breakthrough. We assessed endocrine effects of gonadotropin-releasing hormone agonist (GnRHa) treatment in a prospective cohort of patients aged ≤ 40 years with HR-positive breast cancer. Plasma estradiol (E2), estrone, and follicule-stimulating hormone (FSH) levels were measured from blood samples drawn 1 and 4 years after diagnosis. Patient characteristics, invasive breast cancer-free survival (iBCFS), and overall survival (OS) were compared between those with and without E2 > 2.72 pg/mL during GnRHa treatment. Among eligible patients, 54.7% (46/84) and 60% (15/25) had E2 > 2.72 pg/mL at 1 and 4 years, respectively. Factors associated with E2 > 2.72 pg/mL at 1 year were no prior chemotherapy ( P = 0.045) and tamoxifen use ( P = 0.009). After a median follow-up of 7 years, among patients with stage I-III breast cancer ( N = 74), iBCFS events were seen in 6 (8.1%) with E2 > 2.72 pg/mL and 5 (6.8%) with E2 ≤ 2.72 pg/mL ( P = 0.893). Among patients with de novo metastatic breast cancer ( N = 12), 6 (50%) with E2 > 2.72 pg/mL and 3 (25%) with E2 ≤ 2.72 pg/mL died during follow-up ( P = 0.052). Larger studies exploring the clinical implications of incomplete E2 suppression by GnRHa are needed to ensure optimal OFS treatment strategies are being employed for this population.
Tesch et al. (2024) studied this question.