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125 PROSTATE CANCER INCIDENCE UNDER ANDROGEN DEPRIVATION 8 rates obtained from the Netherlands Comprehensive Cancer Organization (IKNL). 139 Since IKNL generates prostate cancer incidence rates using data from the same source (PALGA), this allows for a reliable comparison. SIRs with 95% confidence intervals (95%CI) were calculated using a Mid-exact P test. Sub-group analyses were performed for trans women who underwent orchiectomy, and for those who did not. For these analyses, follow-up time of people who underwent orchiectomy was calculated from the date of surgery until one of the previously mentioned terminating events. Lastly, SIRs (95%CI) were calculated for different age categories. STATA Statistical Software, version 14.1 (Statacorp, College Station, Texas, USA) and OpenEpi version 3.01 (www.OpenEpi.com) were used for statistical analyses. RESULTS A total of 6,793 individuals were identified, of whom 4,432 were birth-assigned males and 2,361 were birth-assigned females. After applying the inclusion and exclusion criteria, 2,281 trans women were included in this study (Figure 1). The median age at start of hormone treatment was 31 years (IQR 23-41). The median follow-up time was 14 years (IQR 7-24) per person and the total follow-up time of the entire cohort was 37,117 years. Table 1 shows the characteristics of the entire study cohort. 6,793 Transgender people identified 4,512 Excluded 3,004 Never used hormone treatment 11 Unknown start date of hormone treatment 1,366 Trans men 36 Alternating use of female and male hormones 42 <18 years at time of this study 53 Last visit before 1991 2,281 Trans women included Figure 1 . Study flowchart.