Daughters born to mothers who were prescribed the anti-miscarriage drug diethylstilbestrol (DES), a synthetic estrogen, during pregnancy are at increased risk of developing breast cancer, according to research done by a nationwide team of researchers. Between the 1940s through to the 1960s millions of pregnant women were given this drug.

"This is really unwelcome news because so many women worldwide were prenatally exposed to DES, and these women are just now approaching the age at which breast cancer becomes more common," said the study's lead author, Julie Palmer, Sc.D., professor of epidemiology at the Boston University School of Public Health.

For a little history on DES, back in the late 1930s, physicians believed that low levels of estrogen in pregnant women led to spontaneous abortions or premature deliveries. But in the early 1950s, a clinical trial showed no drug benefit in preventing miscarriage. However, use continued in the US until 1971 when researchers determined that DES greatly increased the risk of developing rare cancers of the vagina and cervix in DES daughters.

I assume most DES daughters at increased cancer risk are already aware. However, what makes this news, is that researchers believe that if excess estrogen in utero might increase breast cancer risk later in life, the concern becomes one where other environmental factors that increase fetal exposure to estrogenic compounds need to be given serious consideration.