Abstract PD7-10: Male-GBG54: 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 male breast cancer (BC) patients (pts) have hormone receptor (HR) positive disease. Until today tamoxifen is considered to be the standard of care in male BC pts. Due to the low incidence of male BC, there is a lack of data regarding efficacy and safety. Therapeutic strategies are extrapolated from the standard of care of female BC. However, no prospectively randomized study in male BC pts has been conducted 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 BC patients. Patients and Methods In the phase II Male-GBG54 trial (NCT01638247), pts were randomized to receive either tamoxifen 20 mg/day per os (p.o.) or tamoxifen 20mg/day p.o. + GnRHa subcutaneous (s.c.) q3m or exemestane 25 mg/day p.o. + GnRHa s.c. for 6 months as (neo)adjuvant or metastatic therapy. Further treatment was conducted as per local guidelines. Primary objective was the suppression of oestradiol in the three treatment arms after 3 months of therapy. Secondary objectives comprised oestradiol suppression after six months, compliance and safety of the three therapies, the level of different steroidal hormones (testosterone, dihydrotestosterone, SHBG, FSH, LH) and osteocalcin in the three arms. Quality of Life was assessed using the Aging Male Symptom Score, International Index of Erectile function and International Prostate Symptom Score. Tissue and blood was collected for translational research. Male BC pts with a Karnofsky Index ≥60%, normal blood lipids, and no history or evidence of prostate cancer were eligible. 14 pts per group were needed for the F-test to have 80% power to detect a difference in mean oestradiol decrease between the three therapeutic groups at the 5% significance level. The final sample size was calculated as 48 patients, as a non-parametric test (Kruskal-Wallis) was chosen in case the oestradiol levels are not normally distributed within the study population. Results Between October 2012 and May 2017, 55 pts were randomized within 24 centers in Germany. 52 pts were included in the adjuvant and 2 pts in the metastatic setting of whom 48 pts were fully evaluable and comprised the analysis set. The median age was 62 years (range 37-83 years). The baseline characteristics were well balanced between the 3 treatment groups. Karnofsky Index ranged from 60%-100%, 36.4% had received prior chemotherapy and 12.7% had HER2-positive BC. The majority had a pT2 (52%), pN0 (58.0%) BC. 3 serious adverse events were reported, none was related to the study treatment. Conclusion This is the first prospective randomized trial worldwide evaluating the impact of three different endocrine treatments in male breast cancer. The therapy was well tolerated without safety signals. At the meeting, final results of the primary and secondary endpoints will be present. Citation Format: Reinisch M, Seiler S, Hauzenberger T, Schmatloch S, Strittmatter HJ, Zahm DM, Thode C, Jackisch C, Furlanetto J, Strik D, Stickeler E, Marme F, Janni W, Schmidt M, Kamischke A, Rudlowski C, Nekljudova V, von Minckwitz G, Loibl S. Male-GBG54: 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 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD7-10.