The estrogen paradox

摘要

A randomized controlled trial published in 2006 demonstrated that postmenopausal women who underwent hormone therapy with estrogen alone for a mean of 7.1 years unexpectedly had a decreased risk of breast cancer.1 High doses of estrogen also cause regression of hormone-dependent breast cancers.2 By contrast, a large observational study reported an increased breast cancer risk in women treated with estrogen alone for >20 years.3 We have adopted the term 'estrogen paradox' to highlight the seemingly incongruous nature of these results. In this Viewpoint, we discuss our hypothesis and describe possible mechanisms to account for the observed effects.