A core outcome set for research on masculinizing genital gender-affirming surgery: international consensus results from the GenderCOS project.

Background: Masculinizing genital gender-affirming surgery (gGAS) for transgender and gender diverse people encompasses a complex, heterogenous, and modular set of procedures. To enable evidence-based decision-making or meta-analysis, a uniformity of outcome research is needed. Currently, this is hindered by non-standardized outcome reporting. This study aims to develop a core outcome set (COS) for research on masculinizing gGAS to address this issue. Methods: An international, multidisciplinary study steering group was established, consisting of 16 professional experts (PE) and lived experience experts (LEE), to advise on and support the development of this COS. The steering group convened online on 16 June 2022, 28 September 2023, 2 May 2024, and 29 August 2024. Potential outcomes were identified through interviews and focus groups with LEE and a systematic literature review convened up to September 2023. LEE and PE were recruited globally via websites, social platforms, scientific meetings, patient organizations, and posters and invited to participate in three e-Delphi survey rounds. In the first round, participants rated each outcome's importance on a 5-point Likert scale and provided reasoning for their rating. In subsequent rounds, participants re-rated the outcomes using illustrative quotes and rankings based on prior ratings to refine consensus. Pre-defined criteria guided outcome inclusion and exclusion. A final online consensus meeting with LEE and PE finalized the COS. Findings: Initial outcome gathering identified 384 unique outcomes, of which 38 outcomes were selected for the e-Delphi survey rounds. Thirty-two LEE and 52 PE participants, most from Europe, the UK, and the USA, completed all three survey rounds (February, May, and July 2024). Final consensus was reached in September 2024 on including one clinical outcome, three adverse events, and six patient-reported outcomes in the COS for masculinizing gGAS. The core outcomes are sensibility in the neo-phallus, additional surgery, ability to achieve orgasm, sexual well-being, and satisfaction with neo-genital aesthetics. For urethral lengthening, additional core outcomes include neo-urethral fistula, stricture, and the ability to void while standing. For phalloplasty, additional outcomes are flap necrosis and donor site morbidity. Interpretation: Developing a COS for masculinizing gGAS is a crucial step towards standardized outcome measurement and reporting in clinical research. Implementation could facilitate data comparison, meta-analysis and evidence-based guideline development, ultimately improving personalized surgical care. Funding: None received.