J Clin Endocrinol Metab. 2006 Dec 27; [Epub ahead of print]
Endometrial Effects of Tibolone.
Archer DF, Hendrix S, Gallagher C, Rymer J, Skouby S, Ferenczy A, den Hollander W, et al.
Organon International, Roseland NJ, USA.
Background and objectives: The Tibolone Histology of the Endometrium and Breast Endpoints Study (THEBES) is a multicenter, randomized, double-blind study designed to address the conflicting reports in the literature about the endometrial safety of tibolone(1.25 or 2.5mg/day). Tibolone was compared to continuous combined conjugated equine estrogen (CEE) plus medroxyprogesterone acetate (MPA) (0.625 + 2.5mg/day.
Methods: Subjects were randomized in a 1:1:2 ratio to tibolone 1.25mg/day, 2.5mg/day, and CEE/MPA, respectively. The one-sided 95% confidence interval has been evaluated for the incidence of abnormal endometrial histology (hyperplasia or carcinoma), and hyperplasia and carcinoma separately, for each of the two treatment groups and for the treatment groups combined after one and two years of treatment with tibolone compared to CEE/MPA.
Results: A total of 3,240 women were randomized, with 3,224 receiving at least one dose of study medication. The incidence and upper one-sided 95% confidence interval (CI) for the incidence of abnormal endometrium (hyperplasia or carcinoma), and hyperplasia and carcinoma separately, were calculated at endpoint, year 1 and year 2. The incidence (upper one-sided 95% CI) of abnormal endometrium at endpoint was 0.0 (0.5), 0.0 (0.4) and 0.2 (0.5) in the tibolone 1.25mg, 2.5mg, and CEE/MPA groups, respectively. During the entire treatment period, amenorrhea was reported more frequently with tibolone 1.25mg (78.7%), 2.5mg (71.4%) than with CEE/MPA (44.9%).
Conclusion: The THEBES results confirm previous findings that tibolone does not induce endometrial hyperplasia or carcinoma in postmenopausal women and it is associated with a better vaginal bleeding profile than CEE/MPA.
