According to a Danish study small increases in cancer risk from certain fertility drugs used for longer duration.  The research group identified higher uterine cancer risk among women who had used follicle-stimulating hormone and human menopausal gonadotropin (hMG) for duration longer than 10 years. Similar risk was seen among women who at any point took six or more cycles of clomiphene(treatment for women not ovulating normally) or when clomiphene didn’t work when women were injected with six or more cycles of human chorionic gonadotropin (hCG). Uterine cancer risk seemed about two times the usual risk in each of these scenarios though the absolute risk of developing uterine cancer is still not very high.

The study was based on 16 years of research on a group of 54,362 women who underwent fertility treatment between 1965 and 1998. The 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. 51 and 50 percent of the women who did and did not develop uterine cancer, respectively, used fertility drugs. Differences in risk became clear in investigations of specific fertility drugs used and the length of use. These risks weren’t ruled out when the investigators further allowed for use of a single or multiple fertility drugs, number of births, causes of infertility, and any history of oral contraceptives.