Aims: Bicalutamide, a potent non-steroidal androgen receptor antagonist without off-target effects, is increasingly being used to treat transgender women. However, its comparative efficacy, effect on serum total testosterone concentration and risk of hepatotoxicity in this population is unclear.
Methods: A cross-sectional analysis of patients treated with bicalutamide by the Austin Gender Clinic and private endocrinologists was performed, comparing serum total testosterone concentration, serum estradiol concentration and liver function tests to historical cohorts treated with spironolactone (n=38), cyproterone acetate (n=21) or estradiol without anti-androgen (n=21).
Results: Fourteen patients treated with bicalutamide were identified, with median age 28 (24-40) years and duration of hormone therapy 21 (15-37) months. Median bicalutamide dose was 25 (25-50) mg daily and median duration of bicalutamide therapy was 6 (3-12) months. Four patients commenced bicalutamide at initiation of gender-affirming hormone therapy, while the remaining patients had previous anti-androgen therapy. Median serum total testosterone concentration was 4.5 (0.5-17.8) nmol/L in individuals treated with bicalutamide for >6 months. On univariate analysis, this was not different from individuals treated with cyproterone acetate (0.8 (0.6-1.2) nmol/L, p=0.26), spironolactone (2.0 (0.9-9.4) nmol/L, p=0.76) or estradiol without anti-androgen (10.5 (4.9-17.2) nmol/L, p=0.47). There was no between group difference in serum estradiol concentration (overall p=0.09) or serum ALT (overall p=0.53).
Conclusion: There was no difference in the serum total testosterone concentration in those treated with bicalutamide compared to cyproterone acetate, spironolactone or estradiol without an anti-androgen. Within the bicalutamide group, there was significant variability in serum total testosterone concentration, perhaps attributable to differences in serum estradiol concentration and duration of hormone therapy. It is unclear if this contributes to meaningful differences in feminisation. There was no evidence of hepatotoxicity in our cohort of patients treated with bicalutamide. Prospective studies are required to evaluate the comparative efficacy and long-term safety of bicalutamide in transgender women.