Ovulation-inducing drugs are prescribed to women who have trouble conceiving, are undergoing IVF, or who want to donate or sell their eggs (Image: MBI/Alamy)

DRUGS designed to induce ovulation seem to have increased the risk of uterine cancer in a group of women who were treated with them over 30 years ago.

The number of women who developed the disease after taking the drugs was small. But according to Louise Brinton at the National Cancer Institute in Bethesda, Maryland, who has previously looked at the effects of such drugs, the finding emphasises the need to monitor more women who are treated with them. Brinton was not involved in the latest work.

Ovulation-inducing drugs are prescribed to women who have trouble conceiving, are undergoing IVF, or who want to donate or sell their eggs. Though they have been used for more than 30 years, their health effects are still unclear.

While some studies have linked ovulation-stimulating drugs to an increase in ovarian or breast cancers, others have failed to find any such link. This discrepancy has been blamed on the studies not following women for long enough, or including some who never gave birth; childless women are known to be at increased risk of certain cancers.

Now Ronit Calderon-Margalit at Hadassah-Hebrew University in Jerusalem and colleagues have tackled the problem by comparing cancer incidence in a group of 15,000 Israeli women 30 years after they gave birth. Of the 567 women who reported having been given ovulation-inducing fertility drugs, five developed uterine cancer - which is about three times the incidence in members of the group who had not been given these drugs. For the 362 women who took clomiphene, which tricks the body into making extra eggs by blocking oestrogen receptors, the risk was over four times that of women who did not take the drugs (American Journal of Epidemiology, DOI: 10.1093/aje/kwn318).

There were also smaller but significant increases in breast cancer, malignant melanoma and non-Hodgkin's lymphoma associated with taking the drugs, but not in ovarian cancer.

Jodie Moffat, health information officer at Cancer Research UK, says it is difficult to draw any firm conclusions from the results. "This study didn't include a detailed history of fertility drug use, and the number of women who developed uterine cancer was very small," she says.

Calderon-Margalit accepts that the numbers are small, but says they carry extra weight because they make "biological sense". Tamoxifen, a breast cancer treatment that also blocks oestrogen receptors, is known to increase the risk of uterine cancer.

A spokesman for Sanofi-Aventis, which markets clomiphene, says: "This safety concern had already been debated by experts and so far no formal conclusion has been established." The company "is committed to evaluating any new evidence and discussing with experts and healthcare authorities the appropriate information measures", he adds.