7472 Estrogen Monotherapy for Testosterone Suppression in Gender Diverse Patients

Abstract Disclosure: C. Zhou: None. Q. Jones: None. S. Kokosa: None. C. Kelley: None. Background: For gender diverse individuals assigned male at birth (AMAB), gender-affirming hormone therapy consists of estrogen in combination with anti-androgen medications. Exogenous estrogen use results in the development of feminine secondary sex characteristics while indirectly decreasing testosterone. Anti-androgens such as spironolactone, leuprolide, finasteride, or dutasteride work to further suppress testosterone with successful suppression levels <50ng/dL. However, use of these agents increases the risk of adverse side effects like hyperkalemia, polyuria, and orthostatic hypotension, thus is not suitable for everyone. Anecdotally, estrogen monotherapy has been sufficient in reducing testosterone levels to goal in some patients, however at this time there are no known studies which evaluate estrogen monotherapy and suppression of testosterone. The purpose of this study is to retrospectively review estrogen formulations and dosages in patients who have adequate testosterone suppression in the absence of anti-androgen medications. Methods: The study was a retrospective chart review of adult patients ages 18- 84.99 AMAB receiving gender-affirming estrogen between 9/2020 and 12/2023 seen within an endocrine clinic at a single academic institution. Patients younger than 18, those receiving anti-androgen medications, and those with history of orchiectomy were excluded from the study. Charts were reviewed for estrogen formulations and dosages and total serum testosterone levels. Retrospective chart review will continue with additional data expected in 2024. Results: Ten patients between the ages of 19-81 met the inclusion criteria. Of these, 7 patients identified as transfeminine and 3 identified as nonbinary. The 3 patients who identified as non-binary were not included in analysis as their treatment goals may not align with full feminization or testosterone suppression (total serum testosterone <50ng/dL). Testosterone suppression from estrogen monotherapy was achieved in 100% (n=7) of the transfeminine patients when serum estradiol was >100pg/mL. In those who achieved testosterone suppression, 5 used injectable formulations (estradiol valerate 4-6mg weekly) and 2 used transdermal patches (range of estradiol from 0.2mg twice weekly to 0.3mg three times weekly). Conclusions: Estrogen monotherapy may be effective in suppressing testosterone without the need for anti-androgen medications. So far, this was noted most commonly with use of injectable estrogen formulations. A limitation of the study is the small sample size, however ongoing data collection is anticipated. Additional research evaluating estrogen monotherapy and testosterone suppression is needed and has potentially significant implications for simplified treatment protocols for transfeminine patients. Presentation: 6/2/2024