Impact of Cyproterone Acetate vs Spironolactone on Breast Development in Transgender Care
Overview
This randomized clinical trial compared the effects of cyproterone acetate and spironolactone, combined with estradiol, on breast development in transgender individuals assigned male at birth. After 6 months, no significant difference in breast growth was observed between the two antiandrogens, although cyproterone acetate more effectively suppressed serum testosterone levels.
Background
Transgender individuals assigned male at birth often use antiandrogens alongside estradiol to induce feminization, including breast development. Cyproterone acetate and spironolactone are commonly prescribed antiandrogens with differing mechanisms; cyproterone acetate has stronger androgen receptor antagonism and progestogenic effects leading to greater testosterone suppression. However, evidence comparing their impact on feminization outcomes such as breast growth has been limited. This study aimed to fill that gap by evaluating breast development and hormone suppression over a 6-month period.
Data Highlights
Outcome
Cyproterone Acetate (n=32)
Spironolactone (n=31)
Mean Difference (95% CI)
P Value
Breast–chest distance change (cm)
Not specified
Not specified
0.27 (−0.82 to 1.35)
0.6
Estimated breast volume change (mL)
Not specified
Not specified
17.26 (−16.94 to 51.47)
0.3
Serum testosterone <2 nmol/L (odds ratio)
Higher suppression
Lower suppression
9.01 (1.83 to 44.4)
0.008
Key Findings
No significant difference in breast–chest distance between cyproterone acetate and spironolactone groups after 6 months (mean difference 0.27 cm, P = .6).
No significant difference in estimated breast volume between groups (mean difference 17.26 mL, P = .3).
Cyproterone acetate was significantly more effective at suppressing serum total testosterone to below 2 nmol/L (odds ratio 9.01, P = .008).
Changes in gender dysphoria scores (GPSQ) were similar between the two treatment groups.
Both antiandrogens were administered with standardized estradiol therapy titrated to target serum estradiol levels.
Clinical Implications
Clinicians can select either cyproterone acetate or spironolactone as antiandrogens in feminizing hormone therapy based on patient preference and side effect profiles, as breast development outcomes are comparable. Cyproterone acetate may be preferred when stronger testosterone suppression is desired. Ongoing monitoring and individualized treatment remain essential to optimize feminization outcomes.
Conclusion
This trial demonstrates that while cyproterone acetate achieves greater testosterone suppression than spironolactone, both antiandrogens produce similar breast development when combined with estradiol over 6 months. Antiandrogen choice should be personalized, and further research is needed to enhance feminization strategies.
References
Authors 2020-2022 -- Impact of Cyproterone Acetate and Spironolactone on Mammary Development in Transgender Individuals: A Randomized Clinical Study
