Study results have been contradictory on whether the medications contribute to a rise in ovarian and breast cancers. Scientists have blamed the mixed nature of the findings on the studies’ relatively short length, or on including some childless women (such women are known to have an increased risk of some cancers).
The large recent study was conducted by Ronit Calderon-Margalit at Hadassah-Hebrew University in Jerusalem and her colleagues and appeared in the American Journal of Epidemiology. They compared cancer rates in 15,000 Israeli women 30 years after they gave birth.
In this group, 567 women reported using ovulation-inducing drugs. Among these subjects, five developed uterine cancer – a rate about three times as high as those who hadn’t used the medications. And for the 362 women who took the fertility drug clomiphene, which blocks the brain’s estrogen receptors, tricking the ovaries into making extra eggs, the risk was more than four times that of drug-free women.
The researchers also noted increased rates of breast cancer, malignant melanoma (skin cancer) and non-Hodgkin’s lymphoma, which were smaller but nonetheless significant, in the population of fertility-drug takers. They saw no increase in ovarian cancer.
Despite the size of the study, it’s difficult to draw reliable conclusions, according to Jodie Moffat, health information officer at Cancer Research UK. “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 said.
Calderon-Margalit agreed that the numbers were small, but said the findings are significant because they make “biological sense.” She said it’s known that tamoxifen, a breast cancer medication that also blocks estrogen receptors, increases the incidence of uterine cancer.