A team of US researchers found that these so-called ‘DES daughters’ aged 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. Their findings were published in the journal Cancer Epidemiology, Biomarkers & Prevention.
“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, Dr Julie Palmer, professor of epidemiology at the Boston University School of Public Health.
She said an estimated one to two million women in the US 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 non-exposed 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.
Scientifically, the study may be the first to provide direct evidence that prenatal exposure to excess estrogen may be a risk factor for development of breast cancer, Dr Palmer said.
Although researchers do not know how DES may increase breast cancer risk, Dr Palmer said some scientists believe the excess estrogen increases the number of breast tissue stem cells available at birth – cells that could malignantly transform into cancer.