In contrast to the fairly large number of studies that have investigated the association between fertility drugs and ovarian cancer and breast cancer, only a few epidemiological studies have assessed the link with uterine cancer and findings from these studies have been conflicting. Therefore researchers established a cohort of 54,362 Danish women who attended infertility clinics during the period 1965–1998 to further assess the association between fertility drugs and risk of uterine cancer. A case-cohort study evaluated the effects of different types of fertility drugs on uterine cancer risk.

The following findings were reported:

• Through mid-2006, 83 uterine cancers were identified.

• Ever use of any fertility drug was not associated with uterine cancer risk (rate ratio =1.10, 95% CI; 0.69 to 1.76).

• Ever use of gonadotropins (follicle-stimulating hormone and human menopausal gonadotropin) increased uterine cancer risk (2.21; 1.08 to 4.50); the risk was primarily observed after 10 years of follow-up.

• Uterine cancer risk increased with number of cycles of use for clomiphene (for ≥6 cycles, RR = 1.96; 1.03 to 3.72) and human chorionic gonadotropin (hCG) [for ≥6 cycles, RR = 2.18; 1.16 to 4.08] but not for other gonadotropins.

• Use of gonadotropin-releasing hormone analogues was not associated with risk.

The researchers state that to their knowledge, this cohort represents the largest number of uterine cancer cases included in any infertility cohort study to date. They note that though uterine cancer risk was not associated with ever use of any fertility drug, the findings do show that “infertile women who are treated with gonadotropins, clomiphene, and hCG may have an increased risk of uterine cancer.” They add that since many of the women in the cohort have not yet reached the usual peak age for uterine cancer, they will continue to be monitored to establish a more definite link between fertility drugs and risk of uterine cancer.” Finally, they suggest that “considering the large and increasing number of women being treated every year with fertility drugs, the unfavourable effects of fertility drugs such as increased risk of uterine cancer must always be put into perspective and balanced against the physical and psychological benefits of a pregnancy made possible only through the use of fertility drugs.”