So-called "DES daughters," born to mothers who used the antimiscarriage drug diethylstilbestrol (DES) during pregnancy, are at a substantially greater risk of developing breast cancer compared to women who were not exposed to the drug in utero.
Reporting in a recent issue of the journal Cancer Epidemiology, Biomarkers & Prevention (15:1509-1514, 2006), a nationwide team of researchers found that DES daughters over age 40 had 1.9 times the risk of developing breast cancer, compared to unexposed women of the same age. They also found that the relative risk of developing the cancer was even greater in DES daughters over age 50, but say the number of older women in their study group is, as yet, too small for a firm statistical comparison.
"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, SCD, professor of epidemiology at the Boston University School of Public Health. She said an estimated 1 to 2 million women in the United States were exposed to DES, which was frequently prescribed to women from the 1940s through 1960s to prevent miscarriages.
The ongoing study suggests that DES-exposed women are developing the typical range of breast cancers after age 40 at a faster rate than nonexposed women of the same ages. The researchers also found that the highest relative risk of developing breast cancer was observed in study participants from the cohorts with the highest cumulative doses of DES exposure.
Because of the increased risk observed for DES daughters, the authors urge women who know they were exposed to DES to have regular screening mammograms, and to think twice about using supplemental female hormones.
"DES daughters often ask us about use of these hormones," Palmer said. "It might be wise for exposed women to avoid such supplements. Use of hormone supplements is, in itself, an independent breast cancer risk factor, and women may choose not to compound their already increased risk."
When DES, a synthetic estrogen, was developed in 1938, physicians believed that low levels of estrogen in pregnant women led to spontaneous abortions or premature deliveries. In 1953, a clinical trial indicated no benefit with regard to miscarriage prevention. 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; the Food and Drug Administration subsequently banned use of the drug in pregnant women. Later research demonstrated that DES increased the risk of breast cancer development in mothers who used it.