Diethylstilbestrol (DES) and breast cancer risk

What is DES?

DES (diethylstilbestrol) is a synthetic form of the female hormone, oestrogen. It was prescribed between 1938 and 1971 to help women with certain complications of pregnancy. Use of DES declined following studies in the 1950s that showed it was not effective in preventing pregnancy complications. When given during the first 5 months of a pregnancy, DES can interfere with the development of the reproductive system in a foetus. For this reason, although DES and other estrogens may be prescribed for some medical problems, they are no longer used during pregnancy.