Exposure to the synthetic estrogen diethylstilbestrol (DES) given to women during the 1940s to 1960s to prevent miscarriage and morning sickness increases their risk of breast cancer. But what of the risk to the one to two million daughters born to these women? To determine this, scientists followed 2,000 unexposed and 4,800 exposed daughters for 22 to 24 years, querying them periodically about cancer occurrence and mammogram frequency. The authors found the DES daughters had 1.9 times the risk of breast cancer after age 40 compared to unexposed daughters, with increased risk after age 50. They also found that the women who received the highest cumulative dose of DES exposure in utero had the highest breast cancer risk. Of particular concern were the effects that HRT might have on the DES daughters if they opted for HRT to treat menopause symptoms. "Because the commonly used female hormone supplements have been shown to independently increase risk of breast cancer, it might be wise for exposed women to avoid such supplements whenever possible," the authors wrote. Although DES daughters' breast cancer risk is substantially less than their increased risk of vaginal cancer, the authors worried that their breast cancer risk might rise as they age. They noted that DES daughters often fail to have mammograms regularly. The article appeared in Cancer Epidemiology, Biomarkers Prevention.