Tibolone: cancers of the breast and endometrium.

(1) In 2004, the first results of the British Million Women Study, a prospective cohort study that included more than a million women, showed that women using tibolone had nearly 1.5 times the risk of breast cancer as women who never used hormone replacement therapy. The difference was statistically significant. (2) In 2005, after a mean follow-up of 3.4 years, there were 31 cases of endometrial cancer per 10 000 women who used tibolone. This was almost double the level of risk experienced by women who never used hormone replacement therapy. (3) In another British cohort study, based on a general practice database, the risk of endometrial cancer among 4995 women treated with tibolone was almost double that of women who used sequential estrogen-progestin hormone replacement therapy. (4) Tibolone has no proven advantage over estrogen-progestin hormone combinations for treatment of symptoms of menopause, either in terms of efficacy or cancer risks. It is associated with an increased risk of stroke. There is no justification for using tibolone as a treatment for menopausal symptoms.