Risks and benefits of replacement estrogen.

Many studies show that the risk of a coronary event is reduced by about 50% in postmenopausal women using unopposed oral estrogen compared to women not taking oral estrogens. This protection is biologically plausible, and the magnitude of the benefit would be large if selection factors could be excluded. Studies also show an approximate 50% reduction in hip fracture after three or more years of hormone replacement. An increased risk of endometrial cancer approximately equals the number of years of unopposed estrogen use and continues after estrogen has been discontinued. Use of estrogen for more than five years may increase the risk of breast cancer by 50%, but more data are needed to exclude the effects of selection and diagnostic detection bias. Until clinical trial data are available on estrogen-progestin use, no universal recommendation for hormone replacement or type and duration of treatment can be made.