Diethylstilbestrol (DES) is a synthetic estrogen receptor agonist that was prescribed to pregnant women in the late 1930s. It was banned in 1971 because of possible links to increased risk of breast cancer in mothers along with congenital abnormalities and increased risk of cancer in offspring. DES is structurally related to, and is as potent as, estradiol in most assays, with a longer half-life. It has a relative binding affinity to sex hormone binding globulin (SHBG) of 0.2 compared to estradiol which has a relative binding affinity of 100. A concentration of 20 µM DES, displaces 30 ± 13% of 3H-estradiol from SHBG in serum.