The occurrence of benign brain tumours in transgender individuals during cross-sex hormone treatment.

Benign brain tumours may be hormone sensitive. To induce physical characteristics of the desired gender, transgender individuals often receive cross-sex hormone treatment, sometimes in higher doses than hypogonadal individuals. To date, long-term (side) effects of cross-sex hormone treatment are largely unknown. In the present retrospective chart study we aimed to compare the incidence of common benign brain tumours: meningiomas, pituitary adenomas (non-secretive and secretive), and vestibular schwannomas in transgender individuals receiving cross-sex hormone treatment, with those reported in general Dutch or European populations. This study was performed at the VU University Medical Centre in the Netherlands and consisted of 2555 transwomen (median age at start of cross-sex hormone treatment: 31 years, interquartile range 23-41) and 1373 transmen (median age 23 years, interquartile range 18-31) who were followed for 23 935 and 11 212 person-years, respectively. For each separate brain tumour, standardized incidence ratios with 95% confidence intervals were calculated. In transwomen (male sex assigned at birth, female gender identity), eight meningiomas, one non-secretive pituitary adenoma, nine prolactinomas, and two vestibular schwannomas occurred. The incidence of meningiomas was higher in transwomen than in a general European female population (standardized incidence ratio 4.1, 95% confidence interval 1.9-7.7) and male population (11.9, 5.5-22.7). Similar to meningiomas, prolactinomas occurred more often in transwomen compared to general Dutch females (4.3, 2.1-7.9) and males (26.5, 12.9-48.6). Noteworthy, most transwomen had received orchiectomy but still used the progestogenic anti-androgen cyproterone acetate at time of diagnosis. In transmen (female sex assigned at birth, male gender identity), two cases of somatotrophinomas were observed, which was higher than expected based on the reported incidence rate in a general European population (incidence rate females = incidence rate males; standardized incidence ratio 22.2, 3.7-73.4). Based on our results we conclude that cross-sex hormone treatment is associated with a higher risk of meningiomas and prolactinomas in transwomen, which may be linked to cyproterone acetate usage, and somatotrophinomas in transmen. Because these conditions are quite rare, performing regular screenings for such tumours (e.g. regular prolactin measurements for identifying prolactinomas) seems not necessary.