Importance: 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: This study reports the incidence of prostate cancer in trans women using hormone treatment and thereby shows the long-term effect of androgen deprivation on the initiation and development of prostate cancer.
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: The study was set in the gender identity clinic in Amsterdam where approximately 95% of all transgender people in the Netherlands are treated.
Participants: Trans women who visited our clinic between 1972 and 2016 were identified. 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, who last visited our clinic before 1991, or who used female and male hormones alternatingly, were excluded.
Exposure: For this study, only trans women who received hormone treatment were included.
Main Outcome: 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 reference 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 0.08-0.42).
Conclusions and Relevance: 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.