8614 Low Dose Sublingual Estradiol Decreases Protein S, Generating a Potentially Pro-thrombotic Profile: Interim Results of a Controlled Prospective Pilot Study of Treatment-Naïve Trans Women

Abstract Disclosure: S. Bar On: None. I. Yaish: None. M. Barzilai: None. Y. Greenman: None. G. Gindis: None. Y. Moshe: None. K.M. Tordjman: None. Background: Sublingual estradiol (SLE) for gender-affirming hormone therapy (GAHT) of transgender women (TW) might obviate the need for an anti-androgen, and mitigate pro-coagulant changes. We recently showed that 2 mg E, divided into 4 daily sublingual doses, offers no clinical advantage over the same dose given orally in combination with cyproterone acetate (CPA)[1]. Furthermore, we showed that after each sublingual administration, serum estradiol (sE2) peaked to levels, the likes of which are achieved only during induction of ovulation with gonadotrophins. Hypothesis and Aim: Given the exceedingly high peak sE2 measured under SLE-GAHT, we hypothesized it could lead to partial acquired Protein S deficiency, a recognized pro-thrombotic state and risk factor for venous thromboembolic events (VTE). Our aim was to assess the hemostatic system under SLE in comparison with the standard combined oral (CO) approach. Design and Methods: In this ongoing open label study, treatment-naïve TW are assigned in a 1:1 ratio (15 in each arm) to either standard CO (2 mg E2 with 10 mg CPA once daily), or to SLE with 2 mg sublingual estradiol divided into 4 daily dose for 6 months (6M). An extensive battery of hemostatic biomarkers, including free Protein S antigen (fPS), are assessed at baseline (BL) and at 6M. Results: We herein report on 27 subjects (15 CO/12 SLE) who initiated treatment, 17 of whom have already completed it. The median age of the cohort is 20 y (IQR 19-27; range 18-42]. There were no BL differences between the groups. At 6M, none of the hemostatic markers differed between the groups except for fPS, which was significantly lower in the SLE group 79.7%±11.6% vs. 104.6%±5.6%, P=0.039. By paired comparisons for the entire group, fPS decreased from 104%.2±5.2% at BL to 95.8%±5.9% at 6M, P=0.003. This was entirely accounted for by the change in the SLE group, in which fPS went down from 95.7%±10.3% to 79.7%±11.6%, P