273PD_PRFinal analysis of the Male-GBG54 study: A prospective, randomised multi-centre phase II study evaluating endocrine treatment with either tamoxifen +/- gonadotropin releasing hormone analogue (GnRHa) or an aromatase inhibitor + GnRHa in male breast cancer patients

Background: Over 90% of mBC pts have hormone receptor positive disease. Until today tam is considered the standard of care. Due to the low incidence of mBC, there is a lack of data regarding its efficacy and safety. No prospectively randomized study in mBC pts has been completed so far. The Male-GBG54 study is the first prospective, randomized, multicenter trial evaluating the efficacy and safety of different endocrine treatment options in male pts with BC. Methods: In the Male-GBG54 trial (NCT01638247), pts were randomized to receive tam 20mg/day per os (p.o.) in Arm A, tam + GnRHa subcutaneous (s.c.) q3m in Arm B and exemestane 25 mg/day p.o. + GnRHa s.c. in Arm C for 6 months (mo) as (neo)adjuvant or metastatic therapy. Further treatment was conducted as per local guidelines. Primary objective was the estradiol (E2) suppression after 3 mo. Secondary objectives were the E2 suppression after 6 mo and levels of different steroidal hormones after 3 and 6 mo. Quality of life was assessed using validated questionnaires. 14 pts/group were needed for the F-test to have 80% power to detect a difference in estradiol decrease between the groups at the 5% significance level. Results: Between October 2012 and May 2017, 55 pts were randomized in Germany, of whom 46 pts were fully evaluable and comprised the 6-mo analysis set. The median age was 62 years. Baseline characteristics were well balanced between the 3 arms. The median E2 level with tam increased by 67% after 3 mo and by 41% after 6 mo. In pts receiving tam + GnRH and AI+ GnRH, there was an initial decrease of E2 after 3 mo of 85% and 73% respectively. After 6 mo of therapy the decrease was 59% and 63% respectively. Other hormone parameters will also be presented at the meeting. Conclusions: This is worldwide the first fully recruited prospective randomized trial, evaluating the impact of 3 different endocrine treatments in male BC. The analysis revealed an increase of E2 levels along the course of therapy after an initial steep decrease when GnRHa was given. The therapy was well tolerated with no safety signals. Clinical trial identification: NCT01638247. Legal entity responsible for the study: GBG Forschungs GmbH. Funding: Claudia von Schilling Foundation. Disclosure: C. Jackisch: Travel grants: Celgene, outside the submitted work. V. Moebus: Personal fees: Amgen, Celgene, Roche, Myelotherapeutics, outside the submitted work. F. Marme: Personal fees: Roche, AstraZeneca, Pfizer, Tesaro, Novartis, Amgen, PharmaMar, GenomicHealth, CureVac, Eisai, outside the submitted work. G. von Minckwitz: Research funding to institution: Pfizer, Sanofi, Amgen, Roche, Novartis, Celgene, Teva, Astra Zeneca, Myriad Genetics, Abbvie, Vifor Pharma. S. Loibl: Grants to institution: AbbVie, Amgen, AstraZeneca, Celgene, Novartis, Pfizer, Roche, Teva, Vifor, during the conduct of the study as well as outside the submitted work. All other authors have declared no conflicts of interest.