Women who took diethylstilbestrol (DES) to prevent miscarriages during pregnancy in the Fifties and Sixties have a "statistically significant" increased risk of developing breast cancer (JAMA, 28 April 1993).
Researchers at the Boston University School of Public Health studied a group of 3029 women who had taken DES and an identical number who had not been exposed to the drug. They found 325 cases of breast cancer within the groups, 185 among the DES women and 140 among the unexposed women.
"The incidence rate of breast cancer per 100,000 woman years was 172.3 among exposed women and 134.1 among the unexposed," they concluded.
When other factors, such as age and age when pregnant were taken into account, the relative risk associated with DES exposure was 1.35 times that of those who were not exposed to the drug.
The study did not bear out earlier findings which suggested the risk increases over time.