[Hormone replacement therapy and breast cancer].

An evaluation of the role of estrogen and progesterone in hormone replacement therapy (HRT) as a cause and promotor of breast cancer should begin with a study of the effect of these hormones on normal breast tissue. Cyclic alterations in the histologic changes of the breast in relation to menstruation have been confirmed in some papers. However, the histological influence on the breast of the use of exogenous estrogen and progestin in postmenopausal women remains very controversial. There has been little consistency with regard to the relative risk of HRT and breast cancer in many epidemiological studies. However, the Collaborative. Group on Hormonal Factors in Breast Cancer has brought together and reanalyzed about 90% of the international epidemiological evidence on the relation between risk of breast cancer and use of HRT. These analyses revealed that the risk of breast cancer in HRT users was significantly increased. However, whether HRT affects mortality from breast cancer is unknown.