Current Knowledge of the Effect of Tibolone on the Breast and Uterus: An Extract from the Guidelines for the Use of Tibolone in South Africa
Tibolone is an analogue of the progestin, norethynodrel. After ingestion, it is converted to three metabolites, namely, 3 alpha and 3 beta hydroxytibolone which have oestrogenic effects, and delta 4 isomerase, which has progestogenic and androgenic properties. Both the oestrogenic metabolites bind to the alpha oestrogen receptor, but not the beta oestrogen receptor, whilst the delta 4 isomer binds to the alpha and beta oestrogen, the progestogen and the androgen receptors. Tibolone also is a sulphatase inhibiter, blocking conversion of oestrone sulphate to oestrone, as well as stimulating local sulphotransferase activity. In contrast to other forms of postmenopausal hormonal therapy, it decreases sex hormone binding globulin and hence increases circulating free testosterone, and thereby further adding to its androgenicity. Tibolone significantly decreases vasomotor symptoms, mood disorders, insomnia, bone loss, vaginal atrophy. It has a favourable impact on the cardiovascular system and minimal impact on the endometrium and on mammary tissue. It has been classified as a selective tissue oestrogenic activity regulator, a STEAR.
Tibolone is an important treatment option in the management of the menopause and its specific properties not only relieve the general symptoms of the menopause, but have specific value amongst postmenopausal women with specific conditions. This would include most notably, postmenopausal women with symptoms such as significant malaise and fatigue, marked insomnia, impaired sexual well being, labile moods, excessive breast tenderness or mastalgia.
Women with premature ovarian failure and possibly even the young woman who has been rendered menopausal by surgical bilateral salpingo-oophorectomy would benefit specifically from its use.