Iris de Nie

124 C H A P T E R 8 and Registry of Histopathology and Cytopathology in the Netherlands (PALGA) to obtain data regarding prostate cancer histology and the date of prostate cancer diagnosis. 137 Data with regard to mortality were obtained from Statistics Netherlands (CBS) to calculate follow-up time. 138 The study protocol was assessed by the Ethical Review Board of the VU University Medical Centre Amsterdam. It was concluded that the Medical Research Involving Human Subjects Act (WMO) did not apply to this study, and necessity for informed consent was waived because of the retrospective design and the large study population. Transgender people or the public were not involved in the design, or conduct, or reporting, or dissemination plans of our research. Study population All individuals who visited the gender identity clinic of the Amsterdam UMC between 1972 and 2016 were identified. This cohort has been previously described as the Amsterdam Cohort of Gender Dysphoria. 71 For this study, only trans women who received hormone treatment were included. People who never used hormone treatment, of whom start dates of hormone treatment were unknown, who were under 18 years of age at the time of the study, or who used female and male hormones alternatingly, were excluded. Since data on prostate cancer diagnosis were obtained from PALGA, which covers histopathologic diagnoses since 1991, people were also excluded when their last visit to our clinic was before 1991. 137 The prescribed hormone treatment for trans women generally consisted of a combination of anti-androgens and estrogens. In our cohort, the most commonly prescribed medication to achieve androgen deprivation was cyproterone acetate, only sporadically spironolactone was used. People were advised to discontinue anti-androgenic treatment after bilateral orchiectomy. Types of prescribed estrogens included oestradiol valerate, oestradiol patches, oestradiol gel, ethinyl oestradiol, conjugated estrogens, oestradiol implants, and oestradiol injections. From 2001 onward, mainly oestradiol valerate, oestradiol patches, or oestradiol gel were used. People who were younger than 18 years when they started hormone treatment, had often only used a gonadotropin-releasing hormone agonist, i.e. triptorelin, prior to the start with estrogens. Statistical analysis Characteristics of the cohort are expressed as means with standard deviations (SD) when normally distributed, and as medians with interquartile ranges (IQR) when non-normally distributed. When the cohort consists of less than ten individuals, ranges are given instead of interquartile ranges. To calculate the incidence rate for prostate cancer in our cohort, follow-up time was defined as years from the start date of hormone treatment until either prostate cancer diagnosis, date of death, or the end of the study period (January 25, 2019). To calculate age-adjusted Standardized Incidence Ratios (SIRs), we used the observed cases of prostate cancer and the expected cases based on age-specific incidence