Women whose mothers took the synthetic estrogen Diethylstilbestrol (DES) while pregnant have nearly double the risk of breast cancer. This was the main finding of a study that compared women exposed to DES in utero to a group of comparably aged women who weren't exposed to the excess hormone levels.

DES was prescribed from 1938 through 1971 to prevent miscarriage and other pregnancy complications. During that time, as many as 10 million American women took DES during pregnancy, the US Centers for Disease Control and Prevention estimates.

"Women who were exposed to DES have been wondering about this for a long time," said the study's lead author, Julie Palmer, a professor of epidemiology at Boston University's School of Public Health. "We found the risk of breast cancer was about two times as high in the exposed women compared to unexposed women among those 40 years and older."


Although research published in 1953 refuted the notion that DES could prevent the loss of pregnancy or pregnancy difficulties, doctors still continued to prescribe the drug. In 1971, the US Food and Drug Administration advised doctors to stop prescribing DES because it was linked to a rare form of vaginal and cervical cancer—clear cell adenocarcinoma—in daughters of women who took DES while pregnant. These women eventually came to be known collectively as "DES daughters, according to the CDC.

Previous research had suggested that prenatal hormone levels of DES might affect the risk of breast cancer later in life. And women who took DES have higher rates of breast cancer. So, the researchers behind the new study wanted to assess what the actual risk of breast cancer was for women exposed to DES in utero.

The Study

Researchers recruited 4,817 women who had been exposed to DES in utero in the 1950s and 2,073 women born in the same time period, but who had not been exposed to the drug.

The women completed questionnaires, and 102 women—76 in the DES-exposed group and 26 in the control group-reported a diagnosis of breast cancer.

After compensating for other breast cancer risk factors, the researchers found that women who were exposed to DES in utero had a 91% higher risk for breast cancer after age 40, and a three-fold increased risk for breast cancer after age 50, when compared with women not exposed to the drug.

Reducing Breast Cancer Risk

Dr. Jay Brooks, chairman of hematology and oncology at the Ochsner Health System in Baton Rouge, Louisiana, said, "This is an interesting study that shows we still don't know all of the long-term effects on women who took DES and their female offspring."

Brooks said if women—all women, whether exposed to DES or not—wanted to decrease their risk of breast cancer, they should maintain a normal weight, or lose excess weight.

Palmer added that some research has shown that regular physical activity may be helpful in reducing your risk of breast cancer. Women who know they were exposed to DES in utero should carefully discuss the use of postmenopausal hormones with their doctor, she suggested. Palmer also noted that all women should have regular mammogram screenings to detect breast cancer in its earliest stages.

Depending on what additional risk factors women exposed to DES may have, Brooks said women might want to discuss the potential risks and benefits of using the medications tamoxifen or raloxifene, because these drugs block the action of estrogen, which can fuel some breast tumors.

Chest X-rays Linked To Breast Cancer

In a study of 1,600 women who carry a mutation in the BRCA1 or BRCA2 gene a known breast cancer risk factor), those who reported ever having a chest X-ray were 54% more likely to develop breast cancer than those who had never had one.

Theory: Genetic abnormalities can affect the body's ability to repair DNA damage caused by the ionizing radiation of chest X-rays.

Want to Keep Reading?

Continue reading with a Health Confidential membership.

Sign up now Already have an account? Sign in