What is the role of postmenopausal hormone use in the etiology of breast cancer?

Updated: Dec 26, 2019
  • Author: Graham A Colditz, MD, DrPH; Chief Editor: Chandandeep Nagi, MD  more...
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Postmenopausal estrogens have been used for over half a century. By the mid-1970s, almost 30 million prescriptions were being filled annually in the United States. A challenge in studying the relationship between postmenopausal hormones and breast cancer is the substantial variation in formulations and patterns of use that has occurred over time. By the time sufficient use of one type of hormone has occurred to allow a detailed epidemiologic evaluation, new formulations are already being introduced.

The possible relation between postmenopausal estrogen use and risk of breast cancer has been investigated in over 60 epidemiologic studies over the past 30 years. Most of these studies have been summarized in previous meta-analyses and a large pooled analysis. [41] Subsequently data from randomized controlled trials have confirmed the epidemiologic relations of hormone therapy to increased risk of breast cancer, and the International Agency for Research on Cancer (IARC) has now classified estrogen plus progestin therapy as a human carcinogen. [42] A summary of these findings, plus a more detailed discussion of several of the most important and most recent studies, is provided below. Particular attention is focused on use of estrogen along versus estrogen plus progestin therapy.

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