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115 INCIDENCE OF TESTICULAR CANCER IN TRANS WOMEN USING GENDER-AFFIRMING HORMONAL TREATMENT 7 Figure 2. Follow-up time of study cohort. Dashed line indicates cohort for subgroup analysis performed for trans women with a follow-up time of five years or more. The median age at start of GAHT was 29 years (IQR 22-41). At initiation of GAHT median serum testosterone and estradiol concentrations were in the normal male range. During GAHT median serum estradiol concentrations increased (181 pmol/L, IQR 110-296) and median serum testosterone concentrations decreased (1.0 nmol/L, IQR 0.6-1.3). In this cohort, 1,914 trans women (63%) underwent bilateral orchiectomy a median 2.3 years (IQR 1.7-3.4) after commencing hormonal treatment. Last known hormone measurements before bilateral orchiectomy did not differ from the averaged results during GAHT (data not shown). Table 1 shows the characteristics of the entire study cohort.