Adjuvant endocrine therapy choices in premenopausal patients with hormone receptor-positive early breast cancer: Insights from the prospective GIM23-POSTER study

Background: Most premenopausal patients with early breast cancer (eBC) are diagnosed with hormone receptorpositive disease and therefore candidate for adjuvant endocrine therapy (ET). Patients and methods: The Gruppo Italiano Mammella (GIM) 23-POSTER (GIM23) is a multicenter, prospective, observational study conducted in 26 Italian institutions, aiming to evaluate ET choices for premenopausal patients affected by hormone receptor-positive eBC in a real-world setting. Here we report also the results in terms of type of ET prescribed according to the definition of high-risk patients by monarchE and NATALEE trials. Results: Between October 2019 and June 2022, 600 premenopausal patients were included, with a median age of 46 years. Almost half (271, 45.2 %) of the patients had stage I disease, while 254 (42.3 %) and 60 (10.0 %) patients had stage II and III, respectively. Overall, 149 (25.1 %) patients received tamoxifen alone, 83 (14.0 %) tamoxifen with ovarian function suppression (OFS), while 361 (60.9 %) received aromatase inhibitor (AI) with OFS. Patients treated with AI and OFS had higher number of metastatic axillary nodes, higher grade and more often received chemotherapy (all p < 0.001). According to the inclusion criteria of the monarchE and NATALEE trials, 81 patients (15.6 %) were considered high-risk for the monarchE and received AI with OFS in 88.9% of the cases, while 231 patients (44.4 %) were considered high-risk for the NATALEE trial and received AI with OFS in 74.5% of cases. Conclusions: AI with OFS is the most prescribed adjuvant ET among premenopausal patients, especially in the presence of high-risk features.