Effects of tibolone on the endometrium

OBJECTIVE: To investigate the effects of 24 months of tibolone treatment on the endometrium in postmenopausal women. DESIGN: An open, prospective, multicenter study with a treatment duration of 24 months. POPULATION: One hundred and fifty healthy postmenopausal women. METHODS: Women were treated with one tablet of tibolone (2.5 mg Org OD14) daily. Endometrial biopsies were taken at baseline, 12 months (n = 112) and 24 months (n = 62) to investigate endometrial histology by means of light microscopy. RESULTS: No stimulation of atrophic endometrium was observed in 98.2% and 91.9% of the analyzed women after 12 and 24 months, respectively. A change from an atrophic endometrial pattern to a weakly proliferative pattern was seen in 1.8% (95% confidence interval (CI) 0.22-6.45) and 6.5% (95% CI 1.20-7.51) of the women after 12 and 24 months, respectively. In one woman, the endometrial pattern after 24 months was classified as simple hyperplasia (1.6%; 95% CI 0.01-3.20). The low incidence of proliferation and/or hyperplasia corresponds to that seen in other clinical trials in which women have been treated with placebo. Vaginal bleeding and/or spotting was reported by 18 women (12%), all showing an atrophic endometrium at all assessments, except for one woman with a proliferative endometrium at 24 months. CONCLUSION: In the majority of women (92%), the endometrium remained atrophic during 24 months of tibolone treatment.