Iris de Nie

122 C H A P T E R 8 ABSTRACT Context: Trans women (male sex assigned at birth, female gender identity) mostly use anti-androgens combined with estrogens and can subsequently undergo vaginoplasty including orchiectomy. Because the prostate remains in situ after this procedure, trans women are still at risk for prostate cancer. Objective: The incidence of prostate cancer in trans women using hormone treatment. Design: In this nationwide retrospective cohort study, data of participants were linked to the Dutch national pathology database (PALGA) and to Statistics Netherlands, to obtain data on prostate cancer diagnosis and mortality. Setting: Gender identity clinic. Participants: Trans women who visited our clinic between 1972 and 2016 and received hormone treatment were included. Main Outcome Measures: Standardized incidence ratios (SIRs) were calculated using the number of observed prostate cancer cases in our cohort and the number of expected cases based on age-specific incidence numbers from the Netherlands Comprehensive Cancer Organization. Results: The study population consisted of 2,281 trans women with a median follow-up time of 14 years (interquartile range 7-24), and a total follow-up time of 37,117 years. Six prostate cancer cases were identified after median 17 years of hormone treatment. This resulted in a lower prostate cancer risk in trans women compared to Dutch reference males (SIR 0.20, 95CI 0.08 to 0.42). Conclusions: Trans women receiving androgen deprivation therapy and estrogens have a substantially lower risk for prostate cancer compared to the general male population. Our results support the hypothesis that androgen deprivation has a preventive effect on the initiation and development of prostate cancer.