Introduction Tamoxifen is the only drug known to prevent cancer.
Tamoxifen is a synthetic estrogen which has anti-estrogen effects in certain parts of the body.
In 1977 tamoxifen was approved for women with advanced breast cancer. Further study eventually showed that tamoxifen's anti-estrogen effects could suppress the recurrence of breast cancer in women with early, localized disease. Researchers also noticed that tamoxifen seemed to lower the risk of a new breast cancer occurring in the healthy breast. This experience in breast cancer survivors led some oncologists to propose testing tamoxifen as a preventive in women without breast cancer. Tamoxifen has been proven to increase the risk of endometrial cancer in women with a uterus.