Tamoxifen, originally described as an anti-oestrogen and antifertility agent in the rat, is now a pioneering medicine for the treatment and prevention of breast cancer. Its success is the result of an effective collaboration between laboratory research and clinical trial processes. However, this drug is more than just an anti-oestrogen to treat breast cancer. Laboratory and clinical research defined the concept of selective oestrogen receptor modulation in the 1980s. Non-steroidal anti-oestrogens show oestrogen-like activity in bones and lower cholesterol, but block oestrogen action in the breast and uterus. This realisation led to the development of chemical cousins, known as selective oestrogen receptor modulators. One of these compounds, raloxifene, is used for the prevention of osteoporosis, but is currently being tested as a preventive for breast cancer.