Progestogens in postmenopausal hormone therapy and the risk of breast cancer.

Hormone therapy is the treatment of choice for the alleviation of menopausal symptoms and the treatment of urogenital atrophy. In women with an intact uterus a progestogen must be added to estrogen therapy to prevent endometrial hyperplasia and cancer. There is a wide variety of marketed progestogens which differ in their pharmacological properties according to their structure. Convincing evidence from both clinical trials and epidemiological studies indicates that combined estrogen-progestogen therapy confers a higher risk of breast cancer compared to estrogen monotherapy. Concerning the different types of progestogens, data from large observational studies suggest that natural progesterone and dydrogesterone are associated with a lower risk of breast cancer compared with the other progestins. Observational studies, furthermore, indicate that sequential estrogen-progestogen regimens may lead to a lower risk elevation compared to continuous regimens. The effect of tibolone on breast cancer is unclear. Concluding, both the type of the progestogen and the mode of HT administration may have an impact on breast cancer risk.