Breast cancer and hormone replacement therapy : collaborative reanalysis of data from 51 epidemiological studies involving 52 705 women with breast cancer and 108 411 women without breast cancer

Abstract

For almost half a century various oestrogens and progestagens have been prescribed to replace the cyclical production of ovarian hormones that normally ceases at the menopause. In the early years such hormone replacement therapy (HRT) was mostly in the form of oestrogenic compounds, but other hormones, mostly progestagens, have been increasingly used in combination with oestrogens. The relation between risk of breast cancer and use of HRT has been investigated in many epidemiological studies.1“1 The Collaborative Group on Hormonal Factors in Breast Cancer has brought together and reanalysed the worldwide data on this topic.