Inadequate Ovarian Function Suppression with GnRH Agonists and Subsequent Bilateral Salpingo-Oophorectomy Revealing Ovarian Stromal Hyperplasia in a Premenopausal Woman with Early-Stage, Hormone Receptor-Positive Breast Cancer: A Case Report.

Background: A current standard treatment for pre- or perimenopausal women with high-risk early-stage, hormone receptor-positive breast cancer who have undergone definitive surgery is adjuvant treatment with ovarian function suppression (OFS) with a GnRH agonist (leuprolide or goserelin) with endocrine therapy with an aromatase inhibitor or tamoxifen. Routine measurement of serum estradiol levels for monitoring of OFS during treatment is not a part of current NCCN guidelines. The frequency of estradiol monitoring is therefore often at the discretion of the clinician, and the goal estradiol level is not well established. Case Presentation: We present the case of a 47-year-old female with high-risk early-stage hormone receptor-positive breast cancer who despite use of GnRH agonists did not achieve an estradiol level within the postmenopausal range. She had received two different GnRH agonists (leuprolide and goserelin) and later underwent a bilateral salpingo-oophorectomy (BSO). The pathology showed stromal hyperplasia in both ovaries. After the BSO in April 2024, the GnRH agonist was stopped. The serum estradiol level remained elevated (not in the postmenopausal range) after surgery for 12 months, prior to decreasing to the postmenopausal range. Conclusion: Our patient's clinical course highlights the need for better understanding and establishment of monitoring guidelines for estradiol and the optimal degree of ovarian suppression for patients with breast cancer receiving OFS.