On Dec. 30, 1977, the U.S. Food and Drug Administration approved Tamoxifen, an anti-estrogen drug, for the treatment of breast cancer. Tamoxifen was first synthesized in 1962 by scientists at Imperial Chemical Industries, now known as AstraZeneca.

Tamoxifen is a medication used to treat and prevent breast cancer in women. It is a selective estrogen receptor modulator (SERM), which means it works by blocking the effects of estrogen in certain tissues, such as breast cancer cells.