Abstract PS3-09-25: Factors Associated With Real-World Use of Ovarian Function Suppression Versus Tamoxifen Alone in Premenopausal Women With Early-Stage HR+/HER2- Breast Cancer

Abstract Background Approximately 16% of new breast cancer diagnoses occur in premenopausal women. Young women with estrogen receptor-positive (ER+) human epidermal growth factor receptor 2-negative (HER2–) breast cancer may be considered for adjuvant endocrine therapy (ET) with tamoxifen (Tam) alone or with ovarian function suppression (OFS) plus Tam or aromatase inhibitor (AI). Optimal adjuvant therapy for this population is of significant interest because young age at diagnosis is associated with a worse prognosis. The SOFT and TEXT trials have demonstrated a benefit of OFS compared to Tam alone in premenopausal women with high risk. Use of OFS, however, may be associated with increased toxicity and may be under-utilized in clinical practice. This study evaluated the real-world use of OFS in premenopausal women aged 50 in a large multidisciplinary community breast oncology center. The goal of this study was to investigate factors associated with the use of Tam alone, and to evaluate treatment discontinuation and recurrence rates in women who received Tam alone versus OFS. Methods We analyzed the medical records of premenopausal women (defined as age 50) with Stage 1-3 HR+/HER2– breast cancer from January 2012 to December 2023. We collected demographic, clinicopathologic characteristics, and treatment information. Patients with non-invasive breast cancer, those who did not begin ET, and those who received an aromatase inhibitor (AI) alone were excluded. Results A total of 874 women were diagnosed with early-stage breast cancer at age 50 at our institution between 2012 and 2023. Of these, 723 met eligibility criteria. Median age was 44. The majority were Caucasian (77%), followed by Asian Pacific Islander (10%), Hispanic (5%), Black (5%), and Unknown (3%). 396 (54.8%) underwent mastectomy. 468 (64.7%) received radiation. A genomic assay was used in 49.0% of women. Chemotherapy was administered to 302 (41.8%) women. Adjuvant ET was administered in all women, with 185 patients treated with OFS and 538 treated with Tam alone. When a GnRH agonist was used for OFS, goserelin was used in the majority. Estradiol monitoring on OFS was inconsistently performed but increased in more recent years. A bilateral salpingo-oophorectomy (BSO) was completed in 88 women during their treatment course. Those treated with OFS were more likely to have tumors 3.0 cm, lymph node-positive disease, higher grade tumors, and to have received chemotherapy. A multivariable logistic regression analysis revealed that age at diagnosis and grade were factors significantly associated with the choice of Tam alone versus OFS for adjuvant therapy. ET was discontinued early due to toxicity in 14.5% and 20 patients discontinued ET due to recurrence (16 in the Tam alone group and 4 in the OFS group). At a median follow-up of 66 months, a total of 64 breast cancer recurrences had occurred, 13 in the OFS group and 51 in the Tam alone arm. Recurrence was not statistically different between the OFS and Tam groups when controlling for age, BMI, grade, and stage (HR 0.12 95% CI: 0.60–2.09, p=0.7237). Conclusion Data from the SOFT and TEXT trials support consideration of maximal hormone suppression with OFS in premenopausal women. Our study highlights the likely underutilization of OFS, even in this high-risk population in the community setting, likely due to increased concern for toxicity. However, these concerns are not supported by the increased rate of early discontinuation in the OFS group. Although not statistically significant, a higher number of recurrences were noted in the tamoxifen alone group. Additional research is warranted to optimize the selection of patients who might benefit most from maximal hormonal blockade with OFS compared to Tam alone. Citation Format: P. Saha, C. Sanchez, O. Israel, L. Eldridge, K. Kuchta, K. A. Yao. Factors Associated With Real-World Use of Ovarian Function Suppression Versus Tamoxifen Alone in Premenopausal Women With Early-Stage HR+/HER2- Breast Cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-09-25.