Diethylstilbestrol (DES) (INN, USAN, BAN), also known formerly and inappropriately as stilboestrol (BAN), is a synthetic, non-steroidal estrogen of the stilbestrol group that was first synthesized in 1938. It is also classified as an endocrine disruptor. Human exposure to DES occurred through diverse sources, such as dietary ingestion from supplemented cattle feed and medical treatment for certain conditions, including breast and prostate cancers. From about 1940 to 1971, DES was given to pregnant women in the mistaken belief it would reduce the risk of pregnancy complications and losses.