Effect of long-term testosterone administration on the endometrium of female-to-male (FtM) transsexuals

Introduction. Long term safety of testosterone (T) administration in women is still unknown. In particular few and discordant data exists on the effects of T on the endometrium. Aim. The aim of this study was to investigate the effects of long-term T treatment on endometrium histology and proliferation in female to male transsexual subjects (FtM). We compared these endometria with those of young women in the proliferative phase (PM) of the cycle and with those of post menopausal women (M). Method. Endometrial samples from 27 FtM treated with T (intramuscular injection of 100 mg Testoviron Depot /10 days for at least one year), 30 M undergoing vaginal hysterectomy, and 13 PM undergoing hysteroscopy for infertility problems were collected. Endometrial proliferation was evaluated on the basis of histopathology and expression of the proliferation marker Ki-67. Both M and PM women had not received any hormonal treatment for at least one year. Main Outcome Measure. Circulating total testosterone (TT), estradiol (E), progesterone (P), insulin and glucose levels were measured in FtM and PM subjects. Results. FtM had received T for 33.6 ± 21.3 months (mean ± SD). In FtM subjects, histological analysis found inactive endometrium similar to the atrophic menopausal endometrium. The expression of Ki-67 in the glands, stroma and glands and stroma together was significantly (p < 0.0005) lower in FtM than in PM women and was similar in the FtM and M groups. Small polyps were detected in 5 of the 27 FtM subjects. Conclusions. In conclusion our data suggest that exogenous T administration does not stimulate endometrial proliferation in FtM transsexuals and indeed may have atrophic effects.