The dangers of diethylstilbestrol (DES), a synthetic oestrogen-like hormone given to pregnant women who are at risk of miscarriage, became evident when the daughters of mothers who received the drug developed rare cancers of the cervix and vagina. Exposed mothers were more likely to develop breast cancer, but it was not clear whether their daughters were similarly affected.

A new US study examined the occurrence of breast cancer in a cohort of 4,817 so-called 'DES daughters' compared with 2,073 unexposed women. The key finding, reported in the August issue of Cancer Epidemiology, Biomarkers & Prevention, was that the risk of developing breast cancer was 1.9 times greater in women over the age of 40 who had been exposed to DES in the womb.

According to Julie Palmer, professor of epidemiology at the Boston University School of Public Health and lead researcher on the study: “This is really unwelcome news because so many women worldwide were prenatally exposed to DES and they are just now approaching the age at which breast cancer becomes more common.” (http://www.aacr.org, 7 August 2006).

The findings prompted Palmer to warn affected women to avoid using hormone supplements in later life. Heather Feigelson, senior epidemiologist at the American Cancer Society, also advises caution: “Most of the women in this cohort are now in their early 40s and 50s, and we do not know whether their breast cancer risk will continue to rise.” (http://www.cancer.org, 7 August 2006).

Although DES was withdrawn in 1971, the recent findings underscore the drug's legacy of concern, as expressed by Jane Kevan of the UK campaign group DES Action: “It's another thing to worry about. Where is it all going to end?” (http://news.scotsman.com, 8 August 2006).