9224 Evaluation of Safety and Efficacy of Administration of Estradiol by Subcutaneous Injection in Transgender Women

Abstract Disclosure: H. Perkins: None. H. Moreau: None. J. LaBudde: None. W. Craig: None. D.I. Spratt: None. Background: Off-label use of subcutaneous (SC) estradiol (E2) by transgender women for gender-affirming hormone therapy is becoming increasingly widespread, despite a lack of published data regarding its efficacy and safety. Methods: This retrospective cohort study used manual data extraction from electronic medical records for patients ages 18-79 years, currently or previously receiving oral (PO) 17-beta E2 or SC E2 valerate therapy at Maine Medical Center Reproductive Endocrinology and Infertility and Gender Clinics between 5/30/14-5/30/23, who completed E2 dose adjustments aimed at obtaining a serum E2 of 75-250 pg/mL. SC E2 was administered weekly and PO E2 daily. Serum testosterone (T), estrone (E1), and sex hormone binding globulin (SHBG) levels were recorded if drawn within 90 days of E2 measurement on an optimized dose. In a subset of patients receiving SC E2, serum E2 levels were drawn 1-2 days post- and pre-injection. All patient-reported local or systemic reactions were recorded. Data are expressed as median (full range) or mean ± standard deviation (full range). Results: 45 patients were included with no significant differences in demographics between PO (n=20) and SC (n=25) groups. Both groups achieved therapeutic E2 levels after dose adjustment without statistical difference in mean serum E2 (pg/mL) between SC and PO groups: 148.7 ± 41.0 (78-226) vs. 151.6 ± 31.7 (97-208); p=0.79 by t-test. In patients without orchiectomy, both SC and PO groups had T (ng/dL) suppressed to normal adult female range (10-55) in 11/12 SC patients and in 17/17 PO patients; median T was 14.0 (7.7-86) for SC vs. 20.6 (3.4-42) for PO; p=0.98 by Mann-Whitney U test. Median E2 dose (mg/week) in the SC group was 3.0 (1.4-6.0) and in the PO group was 42.0 (28-84). Median serum E1 (pg/mL) was lower in the SC group than the PO group: 73.5 (29-115), n=12 vs. 907 (596-1601), n=5, p<0.001 by Mann-Whitney U test. E1/E2 ratio was lower in the SC group than the PO group: 0.4 ± 0.1 vs. 8.0 ± 2.9; p<0.001 by t-test. There was no significant difference in median serum SHBG (nmol/L) between SC and PO groups: 71.7 (19.3-146.7), n=15 vs. 73.4 (51.0-187.4), n=14; p=0.20 by Mann-Whitney U test. Mean post- and pre-dose serum E2 levels in 5 patients were 138.0 ± 24.0 and 88.0 ± 57.6, respectively. There was one transient local reaction and no systemic allergic or inflammatory reactions in the SC group with no systemic reactions in the PO group. Conclusion: These results demonstrate that SC E2 at doses of 1.4-6 mg/week can be administered safely to achieve therapeutic serum E2 levels and suppress serum T levels to within the normal female range. Our preliminary data reveal lower serum E1 levels in the SC group than in the PO group suggesting reduced hepatic first-pass metabolism with SC administration; this pattern was not seen with serum SHBG levels. Post- and pre-dose serum E2 levels revealed only a mild decline in E2 levels between injections. Presentation: 6/3/2024