Though the use of fertility drugs does not seem to generally increase uterine cancer risk, a Danish study identified small increases in risk from certain fertility drugs used for longer duration.
Dr. Allan Jensen, with the Danish Cancer Society in Copenhagen, and colleagues identified higher uterine cancer risk among women who used follicle-stimulating hormone and human menopausal gonadotropin (hMG) for more than 10 years.
They saw similar risk among women who ever took six or more cycles of clomiphene, an established treatment for women not ovulating normally, or when clomiphene did not work, when women were injected with six or more cycles of human chorionic gonadotropin (hCG).
In each of these scenarios, uterine cancer risk seemed about two times the usual risk, Jensen and colleagues report in the American Journal of Epidemiology.
Even so, "the absolute risk of developing uterine cancer is still not very high," Jensen emphasized in an email to Reuters Health.
From a group of 54,362 women treated for infertility between 1965 and 1998 and followed for 16 years on average, Jensen's team compared the use of fertility drugs among 83 who developed uterine cancer and 1,241 of similar age who did not develop cancer of the uterus.
Overall, 51 and 50 percent of the women who did and did not develop uterine cancer, respectively, used fertility drugs. Those with uterine cancer ranged from 28 to 67 years old (50 years on average) when diagnosed.
In analyses that allowed for number of births, the investigators did not find significant differences in uterine cancer risk.
Differences in risk, as noted, became evident in analyses of specific fertility drugs used and the length of use. These risks remained when the investigators further allowed for number of births, use of a single or multiple fertility drugs, causes of infertility, and any history of oral contraceptives.
The researchers are continuing to monitor the study group to more definitively assess ties between fertility drugs and uterine cancer risk.
They caution, however, that any unfavorable effects from fertility drugs need to be balanced against the physical and psychological benefits of pregnancies that may only be possible with the use of fertility drugs.
SOURCE: American Journal of Epidemiology, December 1, 2009